bims-unfpre 2023-07-02 papers

bims-unfpre

Biomed News

on Unfolded protein response

Issue of 2023–07–02
fiveteen papers selected by
Susan Logue, University of Manitoba

LncRNAs and CircRNAs in Endoplasmic Reticulum Stress: A Promising Target for Cardiovascular Disease?
A localized hydrogel-mediated chemotherapy causes immunogenic cell death via activation of ceramide-mediated unfolded protein response.
Beyond UPR: Cell-specific Roles of ER Stress Sensor IRE1α in Kidney Ischemic Injury and Transplant Rejection.
Brief Oxygen Exposure after Traumatic Brain Injury Hastens Recovery and Promotes Adaptive Chronic Endoplasmic Reticulum Stress Responses.
Neutrophil extracellular traps aggravate neuronal endoplasmic reticulum stress and apoptosis via TLR9 after traumatic brain injury.
Persistent ER stress causes GPI anchor deficit to convert a GPI-anchored prion protein (PrP) into pro-PrP via the ATF6-miR449c-5p-PIGV axis.
A novel endoplasmic reticulum adaptation is critical for the long-lived Caenorhabditis elegans rpn-10 proteasomal mutant.
Endoplasmic reticulum homeostasis: a potential target for diabetic nephropathy.
The PERK pathway: beneficial or detrimental for neurodegenerative diseases and tumor growth and cancer.
Arginine regulates HSPA5/BiP translation through ribosome pausing in triple-negative breast cancer cells.
The Unfolded Protein Response Sensor IRE1 Regulates Activation of In Vitro Differentiated Type 1 Conventional DCs with Viral Stimuli.
TgMORN2, a MORN Family Protein Involved in the Regulation of Endoplasmic Reticulum Stress in Toxoplasma gondii.
Role of NADPH Oxidase 4 in Corneal Endothelial Cells Is Mediated by Endoplasmic Reticulum Stress and Autophagy.
The unfolded protein response of the endoplasmic reticulum supports mitochondrial biogenesis by buffering non-imported proteins.
Epigenetic regulation of mitochondrial-endoplasmic reticulum dynamics in kidney diseases.

Int J Mol Sci. 2023 Jun 08. pii: 9888. [Epub ahead of print]24(12):

LncRNAs and CircRNAs in Endoplasmic Reticulum Stress: A Promising Target for Cardiovascular Disease?

Francisco José Martinez-Amaro, Carlos Garcia-Padilla, Diego Franco, Houria Daimi.

  The endoplasmic reticulum (ER) is a principal subcellular organelle responsible for protein quality control in the secretory pathway, preventing protein misfolding and aggregation. Failure of protein quality control in the ER triggers several molecular mechanisms such as ER-associated degradation (ERAD), the unfolded protein response (UPR) or reticulophagy, which are activated upon ER stress (ERS) to re-establish protein homeostasis by transcriptionally and translationally regulated complex signalling pathways. However, maintenance over time of ERS leads to apoptosis if such stress cannot be alleviated. The presence of abnormal protein aggregates results in loss of cardiomyocyte protein homeostasis, which in turn results in several cardiovascular diseases such as dilated cardiomyopathy (DCM) or myocardial infarction (MI). The influence of a non-coding genome in the maintenance of proper cardiomyocyte homeostasis has been widely proven. To date, the impact of microRNAs in molecular mechanisms orchestrating ER stress response has been widely described. However, the role of long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) is just beginning to be addressed given the potential role of these RNA classes as therapeutic molecules. Here, we provide a current state-of-the-art review of the roles of distinct lncRNAs and circRNAs in the modulation of ERS and UPR and their impact in cardiovascular diseases.

Keywords:  ER stress; ERAD; UPR; apoptosis; autophagy; cardiovascular diseases; non-coding RNAs

DOI:  https://doi.org/10.3390/ijms24129888
Sci Adv. 2023 Jun 30. 9(26): eadf2746

A localized hydrogel-mediated chemotherapy causes immunogenic cell death via activation of ceramide-mediated unfolded protein response.

Animesh Kar, Dolly Jain, Sandeep Kumar, Kajal Rajput, Sanjay Pal, Kajal Rana, Raunak Kar, Somesh K Jha, Nihal Medatwal, Prabhu Srinivas Yavvari, Nishant Pandey, Devashish Mehta, Harsh Sharma, Debanjan Bhattacharya, Manas K Pradhan, Ravi Datta Sharma, Aasheesh Srivastava, Usha Agrawal, Arnab Mukhopadhyay, Sagar Sengupta, Veena S Patil, Avinash Bajaj, Ujjaini Dasgupta.

Treatment of triple-negative breast cancer (TNBC) is challenging because of its "COLD" tumor immunosuppressive microenvironment (TIME). Here, we present a hydrogel-mediated localized delivery of a combination of docetaxel (DTX) and carboplatin (CPT) (called DTX-CPT-Gel therapy) that ensured enhanced anticancer effect and tumor regression on multiple murine syngeneic and xenograft tumor models. DTX-CPT-Gel therapy modulated the TIME by an increase of antitumorigenic M1 macrophages, attenuation of myeloid-derived suppressor cells, and increase of granzyme B+CD8+ T cells. DTX-CPT-Gel therapy elevated ceramide levels in tumor tissues that activated the protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK)-mediated unfolded protein response (UPR). This UPR-mediated activation of apoptotic cell death led to release of damage-associated molecular patterns, thereby activating the immunogenic cell death that could even clear the metastatic tumors. This study provides a promising hydrogel-mediated platform for DTX-CPT therapy that induces tumor regression and effective immune modulation and, therefore, can be explored further for treatment of TNBC.

DOI: https://doi.org/10.1126/sciadv.adf2746
Kidney Int. 2023 Jun 28. pii: S0085-2538(23)00470-2. [Epub ahead of print]

Beyond UPR: Cell-specific Roles of ER Stress Sensor IRE1α in Kidney Ischemic Injury and Transplant Rejection.

Longhui Qiu, Xin Zheng, Dinesh Jaishankar, Richard Green, Deyu Fang, Satish Nadig, Zheng Jenny Zhang.

  Kidney damage due to ischemia or rejection results in the accumulation of unfolded and misfolded proteins in the endoplasmic reticulum (ER) lumen, a condition known as "ER stress". Inositol-requiring enzyme 1α (IRE1α), the first ER stress sensor found, is a type I transmembrane protein with kinase and endoribonuclease activity. Upon activation, IRE1α non-conventionally splices an intron from unspliced X-box binding protein 1 (XBP1u) mRNA to produce XBP1s mRNA that encodes the transcription factor, XBP1s, for the expression of genes encoding proteins that mediate the unfolded protein response (UPR). The UPR promotes the functional fidelity of ER and is required for secretory cells to sustain protein folding and secretory capability. Prolonged ER stress can lead to apoptosis, which may result in detrimental repercussions to organ health and has been implicated in the pathogenesis and progression of kidney diseases. The IRE1α-XBP1 signaling acts as a major arm of UPR and is involved in regulating autophagy, cell differentiation, and cell death. IRE1α also interacts with Activator Protein-1 (AP-1) and Nuclear Factor-κB (NF-κB) pathways to regulate inflammatory responses. Studies using transgenic mouse models highlight that the roles of IRE1α differ depending on cell type and disease setting. This review covers these cell-specific roles of IRE1α signaling and the potential for therapeutic targeting of this pathway in the context of ischemia and rejection affecting the kidneys.

Keywords:  Acute kidney injury; Cell signaling; Cell survival; Endoplasmic reticulum; Transplantation

DOI:  https://doi.org/10.1016/j.kint.2023.06.016
Int J Mol Sci. 2023 Jun 06. pii: 9831. [Epub ahead of print]24(12):

Brief Oxygen Exposure after Traumatic Brain Injury Hastens Recovery and Promotes Adaptive Chronic Endoplasmic Reticulum Stress Responses.

Jordyn N Torrens, Shelby M Hetzer, Nathan K Evanson.

  Traumatic brain injury (TBI) is a major public health concern, particularly in adolescents who have a higher mortality and incidence of visual pathway injury compared to adult patients. Likewise, we have found disparities between adult and adolescent TBI outcomes in rodents. Most interestingly, adolescents suffer a prolonged apneic period immediately post-injury, leading to higher mortality; therefore, we implemented a brief oxygen exposure paradigm to circumvent this increased mortality. Adolescent male mice experienced a closed-head weight-drop TBI and were then exposed to 100% O2 until normal breathing returned or recovered in room air. We followed mice for 7 and 30 days and assessed their optokinetic response; retinal ganglion cell loss; axonal degeneration; glial reactivity; and retinal ER stress protein levels. O2 reduced adolescent mortality by 40%, improved post-injury visual acuity, and reduced axonal degeneration and gliosis in optical projection regions. ER stress protein expression was altered in injured mice, and mice given O2 utilized different ER stress pathways in a time-dependent manner. Finally, O2 exposure may be mediating these ER stress responses through regulation of the redox-sensitive ER folding protein ERO1α, which has been linked to a reduction in the toxic effects of free radicals in other animal models of ER stress.

Keywords:  adolescent; endoplasmic reticulum stress; neurodegeneration; traumatic brain injury; traumatic optic neuropathy

DOI:  https://doi.org/10.3390/ijms24129831
Cell Death Dis. 2023 06 26. 14(6): 374

Neutrophil extracellular traps aggravate neuronal endoplasmic reticulum stress and apoptosis via TLR9 after traumatic brain injury.

Liang Mi, Xiaobin Min, Mingming Shi, Liang Liu, Yanfeng Zhang, Yanlin Zhu, Peng Li, Yan Chai, Fanglian Chen, Quanjun Deng, Shu Zhang, Jianning Zhang, Xin Chen.

Endoplasmic reticulum (ER) stress and ER stress-mediated apoptosis play an important role during secondary brain damage after traumatic brain injury (TBI). Increased neutrophil extracellular traps (NETs) formation has been demonstrated to be associated with neurological damage after TBI. However, the correlation between ER stress and NETs remains unclear, and the specific function of NETs in neurons has not been defined. In this study, we found that the levels of NETs circulating biomarkers were remarkably elevated in the plasma of TBI patients. We then inhibited NETs formation by peptidylarginine deiminase 4 (PAD4, a critical enzyme for NETs formation) deficiency and discovered that ER stress activation and ER stress-mediated neuronal apoptosis were reduced. The degradation of NETs via DNase I showed similar outcomes. Furthermore, overexpression of PAD4 aggravated neuronal ER stress and ER stress-associated apoptosis, while TLR9 antagonist administration abrogated the damage caused by NETs. In addition to in vivo experiments, in vitro experiments revealed that treatment with a TLR9 antagonist alleviated NETs-induced ER stress and apoptosis in HT22 cells. Collectively, our results indicated that ER stress as well as the accompanying neuronal apoptosis can be ameliorated by disruption of NETs and that suppression of the TLR9-ER stress signaling pathway may contribute to positive outcomes after TBI.

DOI: https://doi.org/10.1038/s41419-023-05898-7
J Biol Chem. 2023 Jun 28. pii: S0021-9258(23)02010-0. [Epub ahead of print] 104982

Persistent ER stress causes GPI anchor deficit to convert a GPI-anchored prion protein (PrP) into pro-PrP via the ATF6-miR449c-5p-PIGV axis.

JingFeng Li, SaSa Li, ShuPei Yu, Jie Yang, JingRu Ke, Huan Li, Heng Chen, MingJian Lu, Man-Sun Sy, ZhenXing Gao, Chaoyang Li.

  ER stress and UPR are cells' survival strategies to thwart disruption of proteostasis. Tumor cells are continuously being challenged by ER stress. The prion protein, PrP, normally a GPI-anchored protein exists as a pro-PrP retaining its GPI-peptide signal sequence in human pancreatic ductal cell adenocarcinoma (PDAC). Higher-abundance of pro-PrP indicates poorer prognosis in PDAC patients. The reason why PDAC cells express pro-PrP is unknown. Here, we report that persistent ER stress causes conversion of GPI-anchored PrP to pro-PrP via a conserved ATF6-microRNA449c-5p-PIGV axis. Mouse neurons and AsPC-1, a PDAC cell line, express GPI-anchored PrP. However, continuous culture of these cells with the ER stress inducers thapsigargin or Brefeldin A results in conversion of a GPI-anchored PrP to pro-PrP. Such a conversion is reversible, removal of the chemical inducers allows the cells to re-express a GPI-anchored PrP. Mechanistically, persistent ER stress increases the abundance of an active ATF6, which then increases the level of microRNA449c-5p (miR449c-5p). By binding the mRNA of PIGV at its 3'-untranslated regions, miR449c-5p suppresses the level of PIGV. As a manosytransferase pivotal in the synthesis of the GPI anchor core, reduction of PIGV leads to disruption of the GPI-anchor assembly, causing pro-PrP accumulation and enhancing cancer cell migration and invasion. The importance of ATF6-miR449c-5p-PIGV axis is recapitulated in PDAC biopsies as the higher-levels of ATF6 and miR449c-5p, and lower-level of PIGV are markers of poorer outcome for patients with PDAC. Drugs targeting this axis may prevent PDAC progression.

Keywords:  ER stress; GPI-anchored proteins; PDAC; Prion protein; Unfolded protein response; microRNA; pro-protein

DOI:  https://doi.org/10.1016/j.jbc.2023.104982
Biochim Biophys Acta Gene Regul Mech. 2023 Jun 22. pii: S1874-9399(23)00052-4. [Epub ahead of print] 194957

A novel endoplasmic reticulum adaptation is critical for the long-lived Caenorhabditis elegans rpn-10 proteasomal mutant.

Meghna N Chinchankar, William B Taylor, Su-Hyuk Ko, Ellen C Apple, Karl A Rodriguez, Lizhen Chen, Alfred L Fisher.

  The loss of proteostasis due to reduced efficiency of protein degradation pathways plays a key role in multiple age-related diseases and is a hallmark of the aging process. Paradoxically, we have reported that the Caenorhabditis elegans rpn-10(ok1865) mutant, which lacks the RPN-10/RPN10/PSMD4 subunit of the 19S regulatory particle of the 26S proteasome, exhibits enhanced cytosolic proteostasis, elevated stress resistance and extended lifespan, despite possessing reduced proteasome function. However, the response of this mutant against threats to endoplasmic reticulum (ER) homeostasis and proteostasis was unknown. Here, we find that the rpn-10 mutant is highly ER stress resistant compared to the wildtype. Under unstressed conditions, the ER unfolded protein response (UPR) is activated in the rpn-10 mutant as signified by increased xbp-1 splicing. This primed response appears to alter ER homeostasis through the upregulated expression of genes involved in ER protein quality control (ERQC), including those in the ER-associated protein degradation (ERAD) pathway. Pertinently, we find that ERQC is critical for the rpn-10 mutant longevity. These changes also alter ER proteostasis, as studied using the C. elegans alpha-1 antitrypsin (AAT) deficiency model, which comprises an intestinal ER-localised transgenic reporter of an aggregation-prone form of AAT called ATZ. The rpn-10 mutant shows a significant reduction in the accumulation of the ATZ reporter, thus indicating that its ER proteostasis is augmented. Via a genetic screen for suppressors of decreased ATZ aggregation in the rpn-10 mutant, we then identified ecps-2/H04D03.3, a novel ortholog of the proteasome-associated adaptor and scaffold protein ECM29/ECPAS. We further show that ecps-2 is required for improved ER proteostasis as well as lifespan extension of the rpn-10 mutant. Thus, we propose that ECPS-2-proteasome functional interactions, alongside additional putative molecular processes, contribute to a novel ERQC adaptation which underlies the superior proteostasis and longevity of the rpn-10 mutant.

Keywords:  Caenorhabditis elegans; ECPS-2/ECM29/ECPAS; Endoplasmic reticulum (ER); Proteasome; RPN-10/RPN10/PSMD4

DOI:  https://doi.org/10.1016/j.bbagrm.2023.194957
Front Endocrinol (Lausanne). 2023 ;14 1182848

Endoplasmic reticulum homeostasis: a potential target for diabetic nephropathy.

Ming Yang, Chongbin Liu, Na Jiang, Yan Liu, Shilu Luo, Chenrui Li, Hao Zhao, Yachun Han, Wei Chen, Li Li, Li Xiao, Lin Sun.

  The endoplasmic reticulum (ER) is the most vigorous organelle in intracellular metabolism and is involved in physiological processes such as protein and lipid synthesis and calcium ion transport. Recently, the abnormal function of the ER has also been reported to be involved in the progression of kidney disease, especially in diabetic nephropathy (DN). Here, we reviewed the function of the ER and summarized the regulation of homeostasis through the UPR and ER-phagy. Then, we also reviewed the role of abnormal ER homeostasis in residential renal cells in DN. Finally, some ER stress activators and inhibitors were also summarized, and the possibility of maintaining ER homeostasis as a potential therapeutic target for DN was discussed.

Keywords:  ER stress; ER-phagy; UPR; diabetic nephropathy; endoplasmic reticulum (ER)

DOI:  https://doi.org/10.3389/fendo.2023.1182848
Hum Mol Genet. 2023 Jun 29. pii: ddad103. [Epub ahead of print]

The PERK pathway: beneficial or detrimental for neurodegenerative diseases and tumor growth and cancer.

Gourango Talukdar, Harry T Orr, Zhixin Lei.

  Protein kinase R (PKR)-like endoplasmic reticulum (ER) kinase (PERK) is one of three major sensors in the unfolded protein response (UPR). The UPR is involved in the modulation of protein synthesis as an adaptive response. Prolonged PERK activity correlates with the development of diseases and the attenuation of disease severity. Thus, the current debate focuses on the role of the PERK signaling pathway either in accelerating or preventing diseases such as neurodegenerative diseases, myelin disorders, and tumor growth and cancer. In this review, we examine the current findings on the PERK signaling pathway and whether it is beneficial or detrimental for the above-mentioned disorders.

Keywords:  Cancer; Demyelination; Neurodegeneration; PERK; eIF2α

DOI:  https://doi.org/10.1093/hmg/ddad103
Br J Cancer. 2023 Jun 29.

Arginine regulates HSPA5/BiP translation through ribosome pausing in triple-negative breast cancer cells.

Christina M Vidal, Ching Ouyang, Yue Qi, Carlos Mendez-Dorantes, Alaysia Coblentz, Jackelyn A Alva-Ornelas, Jeremy M Stark, Victoria L Seewaldt, David K Ann.

BACKGROUND: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with a high mortality rate due to a lack of therapeutic targets. Many TNBC cells are reliant on extracellular arginine for survival and express high levels of binding immunoglobin protein (BiP), a marker of metastasis and endoplasmic reticulum (ER) stress response.
METHODS: In this study, the effect of arginine shortage on BiP expression in the TNBC cell line MDA-MB-231 was evaluated. Two stable cell lines were generated in MDA-MB-231 cells: the first expressed wild-type BiP, and the second expressed a mutated BiP free of the two arginine pause-site codons, CCU and CGU, termed G-BiP.
RESULTS: The results showed that arginine shortage induced a non-canonical ER stress response by inhibiting BiP translation via ribosome pausing. Overexpression of G-BiP in MDA-MB-231 cells promoted cell resistance to arginine shortage compared to cells overexpressing wild-type BiP. Additionally, limiting arginine led to decreased levels of the spliced XBP1 in the G-BiP overexpressing cells, potentially contributing to their improved survival compared to the parental WT BiP overexpressing cells.
CONCLUSION: In conclusion, these findings suggest that the downregulation of BiP disrupts proteostasis during arginine shortage-induced non-canonical ER stress and plays a key role in cell growth inhibition, indicating BiP as a target of codon-specific ribosome pausing upon arginine shortage.

DOI: https://doi.org/10.1038/s41416-023-02322-x
Int J Mol Sci. 2023 Jun 16. pii: 10205. [Epub ahead of print]24(12):

The Unfolded Protein Response Sensor IRE1 Regulates Activation of In Vitro Differentiated Type 1 Conventional DCs with Viral Stimuli.

Bernardita Medel, José Ignacio Bernales, Alonso Lira, Dominique Fernández, Takao Iwawaki, Pablo Vargas, Fabiola Osorio.

  Type 1 conventional dendritic cells (cDC1s) are leukocytes competent to coordinate antiviral immunity, and thus, the intracellular mechanisms controlling cDC1 function are a matter of intense research. The unfolded protein response (UPR) sensor IRE1 and its associated transcription factor XBP1s control relevant functional aspects in cDC1s including antigen cross-presentation and survival. However, most studies connecting IRE1 and cDC1 function are undertaken in vivo. Thus, the aim of this work is to elucidate whether IRE1 RNase activity can also be modeled in cDC1s differentiated in vitro and reveal the functional consequences of such activation in cells stimulated with viral components. Our data show that cultures of optimally differentiated cDC1s recapitulate several features of IRE1 activation noticed in in vivo counterparts and identify the viral analog Poly(I:C) as a potent UPR inducer in the lineage. In vitro differentiated cDC1s display constitutive IRE1 RNase activity and hyperactivate IRE1 RNase upon genetic deletion of XBP1s, which regulates production of the proinflammatory cytokines IL-12p40, TNF-α and IL-6, Ifna and Ifnb upon Poly(I:C) stimulation. Our results show that a strict regulation of the IRE1/XBP1s axis regulates cDC1 activation to viral agonists, expanding the scope of this UPR branch in potential DC-based therapies.

Keywords:  IRE1; cDC1s; dendritic cells; proinflammatory cytokines; unfolded protein response

DOI:  https://doi.org/10.3390/ijms241210205
Int J Mol Sci. 2023 Jun 16. pii: 10228. [Epub ahead of print]24(12):

TgMORN2, a MORN Family Protein Involved in the Regulation of Endoplasmic Reticulum Stress in Toxoplasma gondii.

Jinxuan Li, Qianqian Xiao, Qianqian Tan, Junpeng Chen, Lingyu Sun, Xiao Chen, Ziyu Chu, Hongxia Wu, Zhenzhao Zhang, Hongmei Li, Xiaomin Zhao, Xiao Zhang.

  MORN proteins play a key role in the cytoskeletal structure of eukaryotes and are essential for the close arrangement of the endoplasmic reticulum and plasma membrane. A gene with nine MORN motifs (TGGT1_292120, named TgMORN2) was identified in the Toxoplasma gondii genome; it was presumed to belong to the MORN protein family and to have the function of forming the cytoskeleton, which affects the survival of T. gondii. However, the genetic deletion of MORN2 did not noticeably affect parasite growth and virulence. Using adjacent protein labeling techniques, we identified a network of TgMORN2 interactions, which mainly included endoplasmic reticulum stress (ER stress)-related proteins. In exploring these data, we found that the pathogenicity of the KO-TgMORN2 strain was significantly reduced in the case of tunicamycin-induced ER stress. Reticulon TgRTN (TGGT1_226430) and tubulin β-Tubulin were identified as interaction proteins of TgMORN2. Collectively, TgMORN2 plays a role in ER stress, which lays a foundation for further research on the function of the MORN protein in T. gondii.

Keywords:  TgMORN2; Toxoplasma gondii; endoplasmic reticulum stress

DOI:  https://doi.org/10.3390/ijms241210228
Antioxidants (Basel). 2023 Jun 07. pii: 1228. [Epub ahead of print]12(6):

Role of NADPH Oxidase 4 in Corneal Endothelial Cells Is Mediated by Endoplasmic Reticulum Stress and Autophagy.

Dae Joong Ma, Jin Sun Hwang, Kyung Bo Noh, Sun-Hee Oh, Kyoung Wook Kim, Young Joo Shin.

  Human corneal-endothelial cells (hCEnCs) are located on the inner layer of the cornea. Injury to CEnCs leads to permanent corneal edema, requiring corneal transplantation. NADPH oxidase 4 (NOX4) has been reported to be implicated in the pathogenesis of CEnCs diseases. Thus, we investigated the role of NOX4 in CEnCs in this study. In an animal study, siRNA for NOX4 (siNOX4) or plasmid for NOX4 (pNOX4) was introduced into the corneal endothelium of rats by electroporation, using a square-wave electroporator (ECM830, Havard apparatus) to decrease or increase the expression of NOX4, respectively, and the rat corneas were cryoinjured through contact with a metal rod of 3 mm diameter frozen in liquid nitrogen for 10 min. The immunofluorescence staining of NOX4 and 8-OHdG showed that the levels of NOX4 and 8-OHdG were decreased in the siNOX4 group compared to the siControl, and increased in the pNOX4 group compared to the pControl at one week after treatment. Without cryoinjury, corneal opacity was more severe, and the density of CEnCs was lower, in pNOX4-treated rats compared to pControl. After cryoinjury, the corneas were more transparent, and the CEnC density was higher, in siNOX4-treated rats. The hCEnCs were cultured and transfected with siNOX4 and pNOX4. The silencing of NOX4 in hCEnCs resulted in a normal cell shape, higher viability, and higher proliferation rate than those transfected with the siControl, while NOX4 overexpression had the opposite effect. NOX4 overexpression increased the number of senescent cells and intracellular oxidative stress levels. NOX4 overexpression increased ATF4 and ATF6 levels, and nuclear translocation of XBP-1, which is the endoplasmic reticulum (ER) stress marker, while the silencing of NOX4 had the opposite effect. Additionally, the mitochondrial membrane potential was hyperpolarized by the silencing of NOX4, and depolarized by NOX4 overexpression. The LC3II levels, a marker of autophagy, were decreased by the silencing of NOX4, and increased by NOX4 overexpression. In conclusion, NOX4 plays a pivotal role in the wound-healing and senescence of hCEnCs, by modulating oxidative stress, ER stress, and autophagy. The regulation of NOX4 may be a potential therapeutic strategy for regulating the homeostasis of CEnCs, and treating corneal-endothelial diseases.

Keywords:  NOX4; autophagy; corneal-endothelial cells; in vivo transfection; reactive oxygen species; senescence

DOI:  https://doi.org/10.3390/antiox12061228
Mol Biol Cell. 2023 Jun 28. mbcE23050205

The unfolded protein response of the endoplasmic reticulum supports mitochondrial biogenesis by buffering non-imported proteins.

Katharina Knöringer, Carina Groh, Lena Krämer, Kevin C Stein, Katja G Hansen, Jannik Zimmermann, Bruce Morgan, Johannes M Herrmann, Judith Frydman, Felix Boos.

Almost all mitochondrial proteins are synthesized in the cytosol and subsequently targeted to mitochondria. The accumulation of non-imported precursor proteins occurring upon mitochondrial dysfunction can challenge cellular protein homeostasis. Here we show that blocking protein translocation into mitochondria results in the accumulation of mitochondrial membrane proteins at the endoplasmic reticulum, thereby triggering the unfolded protein response (UPRER). Moreover, we find that mitochondrial membrane proteins are also routed to the ER under physiological conditions. The level of ER-resident mitochondrial precursors is enhanced by import defects as well as metabolic stimuli that increase the expression of mitochondrial proteins. Under such conditions, the UPRER is crucial to maintain protein homeostasis and cellular fitness. We propose the ER serves as a physiological buffer zone for those mitochondrial precursors that cannot be immediately imported into mitochondria while engaging the UPRER to adjust the ER proteostasis capacity to the extent of precursor accumulation.

DOI: https://doi.org/10.1091/mbc.E23-05-0205
J Cell Physiol. 2023 Jun 25.

Epigenetic regulation of mitochondrial-endoplasmic reticulum dynamics in kidney diseases.

Vishwadeep Shelke, Vinayak Yelgonde, Ajinath Kale, Maciej Lech, Anil Bhanudas Gaikwad.

  Kidney diseases are serious health problems affecting >800 million individuals worldwide. The high number of affected individuals and the severe consequences of kidney dysfunction demand an intensified effort toward more effective prevention and treatment. The pathophysiology of kidney diseases is complex and comprises diverse organelle dysfunctions including mitochondria and endoplasmic reticulum (ER). The recent findings prove interactions between the ER membrane and nearly all cell compartments and give new insights into molecular events involved in cellular mechanisms in health and disease. Interactions between the ER and mitochondrial membranes, known as the mitochondria-ER contacts regulate kidney physiology by interacting with each other via membrane contact sites (MCS). ER controls mitochondrial dynamics through ER stress sensor proteins or by direct communication via mitochondria-associated ER membrane to activate signaling pathways such as apoptosis, calcium transport, and autophagy. More importantly, these organelle dynamics are found to be regulated by several epigenetic mechanisms such as DNA methylation, histone modifications, and noncoding RNAs and can be a potential therapeutic target against kidney diseases. However, a thorough understanding of the role of epigenetic regulation of organelle dynamics and their functions is not well understood. Therefore, this review will unveil the role of epigenetic mechanisms in regulating organelle dynamics during various types of kidney diseases. Moreover, we will also shed light on different stress origins in organelles leading to kidney disease. Henceforth, by understanding this we can target epigenetic mechanisms to maintain/control organelle dynamics and serve them as a novel therapeutic approach against kidney diseases.

Keywords:  endoplasmic reticulum; epigenetics; kidney diseases; mitochondria; organelle dynamics

DOI:  https://doi.org/10.1002/jcp.31058