bims-lypmec 2022-08-21 papers

bims-lypmec

Biomed News

on Lysosomal positioning and metabolism in cardiomyocytes

Issue of 2022‒08‒21
thirteen papers selected by
Satoru Kobayashi
New York Institute of Technology

AAA + ATPase Thorase inhibits mTOR signaling through the disassembly of the mTOR complex 1.
Induction of the ER stress response in NRVMs is linked to cardiotoxicity caused by celastrol.
ER stress and inflammation crosstalk in obesity.
Palmitate and thapsigargin have contrasting effects on ER membrane lipid composition and ER proteostasis in neuronal cells.
Dysregulated autophagic activity induced in response to chronic intermittent hypoxia contributes to the pathogenesis of NAFLD.
ER and Golgi trafficking in axons, dendrites, and glial processes.
Disulfide-crosslink analysis of the ubiquitin ligase Hrd1 complex during endoplasmic reticulum-associated protein degradation.
ORP5 and ORP8 orchestrate lipid droplet biogenesis and maintenance at ER-mitochondria contact sites.
Transplantation of fecal microbiota from APP/PS1 mice and Alzheimer's disease patients enhanced endoplasmic reticulum stress in the cerebral cortex of wild-type mice.
ER stress and UPR in Alzheimer's disease: mechanisms, pathogenesis, treatments.
PERK promotes immunosuppressive M2 macrophage phenotype by metabolic reprogramming and epigenetic modifications through the PERK-ATF4-PSAT1 axis.
Functions and mechanisms of protein disulfide isomerase family in cancer emergence.
Subcellular trafficking and post-translational modification regulate PIN polarity in plants.

Nat Commun. 2022 Aug 17. 13(1): 4836

AAA + ATPase Thorase inhibits mTOR signaling through the disassembly of the mTOR complex 1.

George K E Umanah, Leire Abalde-Atristain, Mohammed Repon Khan, Jaba Mitra, Mohamad Aasif Dar, Melissa Chang, Kavya Tangella, Amy McNamara, Samuel Bennett, Rong Chen, Vasudha Aggarwal, Marisol Cortes, Paul F Worley, Taekjip Ha, Ted M Dawson, Valina L Dawson.

The mechanistic target of rapamycin (mTOR) signals through the mTOR complex 1 (mTORC1) and the mTOR complex 2 to maintain cellular and organismal homeostasis. Failure to finely tune mTOR activity results in metabolic dysregulation and disease. While there is substantial understanding of the molecular events leading mTORC1 activation at the lysosome, remarkably little is known about what terminates mTORC1 signaling. Here, we show that the AAA + ATPase Thorase directly binds mTOR, thereby orchestrating the disassembly and inactivation of mTORC1. Thorase disrupts the association of mTOR to Raptor at the mitochondria-lysosome interface and this action is sensitive to amino acids. Lack of Thorase causes accumulation of mTOR-Raptor complexes and altered mTORC1 disassembly/re-assembly dynamics upon changes in amino acid availability. The resulting excessive mTORC1 can be counteracted with rapamycin in vitro and in vivo. Collectively, we reveal Thorase as a key component of the mTOR pathway that disassembles and thus inhibits mTORC1.

DOI: https://doi.org/10.1038/s41467-022-32365-2
Acta Biochim Biophys Sin (Shanghai). 2022 Aug 25.

Induction of the ER stress response in NRVMs is linked to cardiotoxicity caused by celastrol.

Zhong Chen, Zhong Zhuang, Chen Meng, Zhonghua Zhu, Yin Zhang, Zhao Zhang.

  Celastrol is a quinone methide triterpenoid extracted from the root bark of Tripterygium wilfordii Hook F, and it exhibits extensive biological activities such as anti-cancer effects. However, narrow therapeutic window together with undesired side effects limit its clinical application. In this study, we explore celastrol's cardiotoxicity using the methods of histology and cell biology. The results show that celastrol administration dose-dependently induces cardiac dysfunction in mice as manifested by left ventricular dilation, myocardial interstitial fibrosis, and cardiomyocyte hypertrophy. Exposure to celastrol greatly decreases neonatal rat ventricular myocyte (NRVM) viability and promotes its apoptosis. More importantly, we demonstrate that celastrol exerts its pro-apoptotic effects through endoplasmic reticulum (ER) stress and unfolded protein response. Furthermore, siRNA targeting C/EBP homologous protein, a pivotal component of ER stress-mediated apoptosis, effectively prevents the pro-apoptotic effect of celastrol. Taken together, our results demonstrate the potential cardiotoxicity of celastrol and a direct involvement of ER stress in the celastrol-induced apoptosis of NRVMs. Thus, we recommend careful evaluation of celastrol's cardiovascular effects when using it in the clinic.

Keywords:  cardiotoxicity; celastrol; endoplasmic reticulum stress; neonatal rat ventricular myocytes

DOI:  https://doi.org/10.3724/abbs.2022104
Med Res Rev. 2022 Aug 17.

ER stress and inflammation crosstalk in obesity.

Amir Ajoolabady, Cynthia Lebeaupin, Ne N Wu, Randal J Kaufman, Jun Ren.

  The endoplasmic reticulum (ER) governs the proper folding of polypeptides and proteins through various chaperones and enzymes residing within the ER organelle. Perturbation in the ER folding process ensues when overwhelmed protein folding exceeds the ER handling capacity, leading to the accumulation of misfolded/unfolded proteins in the ER lumen-a state being referred to as ER stress. In turn, ER stress induces a gamut of signaling cascades, termed as the "unfolded protein response" (UPR) that reinstates the ER homeostasis through a panel of gene expression modulation. This type of UPR is usually deemed "adaptive UPR." However, persistent or unresolved ER stress hyperactivates UPR response, which ultimately, triggers cell death and inflammatory pathways, termed as "maladaptive/terminal UPR." A plethora of evidence indicates that crosstalks between ER stress (maladaptive UPR) and inflammation precipitate obesity pathogenesis. In this regard, the acquisition of the mechanisms linking ER stress to inflammation in obesity might unveil potential remedies to tackle this pathological condition. Herein, we aim to elucidate key mechanisms of ER stress-induced inflammation in the context of obesity and summarize potential therapeutic strategies in the management of obesity through maneuvering ER stress and ER stress-associated inflammation.

Keywords:  ER stress; adipocytes; inflammation; insulin resistance; obesity

DOI:  https://doi.org/10.1002/med.21921
Biochim Biophys Acta Mol Cell Biol Lipids. 2022 Aug 15. pii: S1388-1981(22)00109-3. [Epub ahead of print] 159219

Palmitate and thapsigargin have contrasting effects on ER membrane lipid composition and ER proteostasis in neuronal cells.

Maria H Jäntti, Shelley Jackson, Jeffrey Kuhn, Ilmari Parkkinen, Sreesha Sree, Joshua Hinkle, Eija Jokitalo, Leesa Deterding, Brandon K Harvey.

  The endoplasmic reticulum (ER) is an organelle that performs several key functions such as protein synthesis and folding, lipid metabolism and calcium homeostasis. When these functions are disrupted, such as upon protein misfolding, ER stress occurs. ER stress can trigger adaptive responses to restore proper functioning such as activation of the unfolded protein response (UPR). In certain cells, the free fatty acid palmitate has been shown to induce the UPR. Here, we examined the effects of palmitate on UPR gene expression in a human neuronal cell line and compared it with thapsigargin, a known depletor of ER calcium and trigger of the UPR. We used a Gaussia luciferase-based reporter to assess how palmitate treatment affects ER proteostasis and calcium homeostasis in the cells. We also investigated how ER calcium depletion by thapsigargin affects lipid membrane composition by performing mass spectrometry on subcellular fractions and compared this to palmitate. Surprisingly, palmitate treatment did not activate UPR despite prominent changes to membrane phospholipids. Conversely, thapsigargin induced a strong UPR, but did not significantly change the membrane lipid composition in subcellular fractions. In summary, our data demonstrate that changes in membrane lipid composition and disturbances in ER calcium homeostasis have a minimal influence on each other in neuronal cells. These data provide new insight into the adaptive interplay of lipid homeostasis and proteostasis in the cell.

Keywords:  Brain lipids; Cell signaling; ER calcium; Endoplasmic reticulum; Exodosis; Lipidomics; Lipids; Palmitate; Phospholipids; Thapsigargin; UPR; Unfolded protein response

DOI:  https://doi.org/10.1016/j.bbalip.2022.159219
Front Physiol. 2022 ;13 941706

Dysregulated autophagic activity induced in response to chronic intermittent hypoxia contributes to the pathogenesis of NAFLD.

Dong Wang, Dongyu Si, Gang Li, Zhimin Ding, Xiaonan Yang, Chaobing Gao.

  Chronic intermittent hypoxia (CIH) is a pathological characteristic of obstructive sleep apnea (OSA) that has been linked to the pathogenesis of nonalcoholic fatty liver disease (NAFLD). The specific link between CIH, autophagic activity, and NAFLD, however, has not previously been characterized. The goal of this study was to assess the relationship between CIH-induced autophagy and the pathogenesis of OSA-associated NAFLD. Western blotting was used to assess the expression of proteins associated with lipid synthesis, endoplasmic reticulum (ER) stress, and autophagic activity. To establish an in vivo model system, C57BL/6 mice were subjected to CIH conditions for 8 h per day over a 12-week period, and were administered chloroquine (CQ) for 1 week prior to euthanization. Levels of serum and liver triglycerides in these animals were assessed, as were proteins related to hepatic autophagy, ER stress, and lipogenesis. qPCR was additionally used to assess hepatic inflammation-related gene expression, while transmission electron microscopy was used to monitor lipid droplet (LD) accumulation and ER morphology. OSA patients and CIH model mice exhibited increases in the expression of proteins associated with hepatic autophagy, ER stress, and lipogenesis. CIH was also associated with more pronounced LD accumulation, hepatic inflammation, and hepatic steatosis in these mice. While serum and hepatic TG and TC levels and serum ALT/AST were increased in response to CIH treatment, the administration of CQ to these mice led to reductions in ER stress-related proteins (XBP1, IRE1α, EIF2α) and lipogenesis-related proteins (ACC, SCD1, FASn), in addition to significantly reducing hepatic inflammation, steatosis, and LD accumulation in these animals. These results suggest that persistent CIH can drive dysregulated hepatic autophagic activity, hepatic steatosis, and ER stress, highlighting potential targets for therapeutic intervention aimed at preventing or treating OSA-associated NAFLD.

Keywords:  NAFLD; autophagy; chronic intermittent hypoxia; endoplasmic reticulum stress; osa

DOI:  https://doi.org/10.3389/fphys.2022.941706
Curr Opin Cell Biol. 2022 Aug 11. pii: S0955-0674(22)00072-2. [Epub ahead of print]78 102119

ER and Golgi trafficking in axons, dendrites, and glial processes.

Shahrnaz Kemal, Hunter S Richardson, Eric D Dyne, Meng-Meng Fu.

Both neurons and glia in mammalian brains are highly ramified. Neurons form complex neural networks using axons and dendrites. Axons are long with few branches and form pre-synaptic boutons that connect to target neurons and effector tissues. Dendrites are shorter, highly branched, and form post-synaptic boutons. Astrocyte processes contact synapses and blood vessels in order to regulate neuronal activity and blood flow, respectively. Oligodendrocyte processes extend toward axons to make myelin sheaths. Microglia processes dynamically survey their environments. Here, we describe the local secretory system (ER and Golgi) in neuronal and glial processes. We focus on Golgi outpost functions in acentrosomal microtubule nucleation, cargo trafficking, and protein glycosylation. Thus, satellite ER and Golgi are critical for local structure and function in neurons and glia.

DOI: https://doi.org/10.1016/j.ceb.2022.102119
J Biol Chem. 2022 Aug 12. pii: S0021-9258(22)00816-X. [Epub ahead of print] 102373

Disulfide-crosslink analysis of the ubiquitin ligase Hrd1 complex during endoplasmic reticulum-associated protein degradation.

Rudolf Pisa, Tom A Rapoport.

  Misfolded proteins in the lumen of the endoplasmic reticulum (ER) are retro-translocated into the cytosol and degraded by the ubiquitin-proteasome system, a pathway termed luminal ER-associated protein degradation (ERAD-L). Retro-translocation is mediated by a conserved protein complex, consisting of the ubiquitin ligase Hrd1 and four associated proteins (Der1, Usa1, Hrd3, and Yos9). Photo-crosslinking experiments provided preliminary evidence for the polypeptide path through the membrane, but did not reveal specific interactions between amino acids in the substrate and Hrd1 complex. Here, we have used site-specific disulfide crosslinking to map the interactions of a glycosylated model substrate with the Hrd1 complex in live S. cerevisiae cells. Together with available electron cryo-microscopy (cryo-EM) structures, the results show that the substrate interacts on the luminal side with both a groove in Hrd3 and the lectin domain of Yos9, and inserts a loop into the membrane, with one side of the loop interacting with the lateral gate of Der1, and the other with the lateral gate of Hrd1. Our disulfide crosslinking experiments also show that two Hrd1 molecules can interact through their lateral gates, and that Hrd1 auto-ubiquitination is required for the disassembly of these Hrd1 dimers. Taken together, these data define the path of a polypeptide through the ER membrane and suggest that auto-ubiquitination of inactive Hrd1 dimers is required to generate active Hrd1 monomers.

Keywords:  Der1; ERAD; Hrd1; Hrd3; Usa1; Yos9; crosslinking; disulfide; retrotranslocation

DOI:  https://doi.org/10.1016/j.jbc.2022.102373
J Cell Biol. 2022 Sep 05. pii: e202112107. [Epub ahead of print]221(9):

ORP5 and ORP8 orchestrate lipid droplet biogenesis and maintenance at ER-mitochondria contact sites.

Valentin Guyard, Vera Filipa Monteiro-Cardoso, Mohyeddine Omrane, Cécile Sauvanet, Audrey Houcine, Claire Boulogne, Kalthoum Ben Mbarek, Nicolas Vitale, Orestis Faklaris, Naima El Khallouki, Abdou Rachid Thiam, Francesca Giordano.

Lipid droplets (LDs) are the primary organelles of lipid storage, buffering energy fluctuations of the cell. They store neutral lipids in their core that is surrounded by a protein-decorated phospholipid monolayer. LDs arise from the endoplasmic reticulum (ER). The ER protein seipin, localizing at ER-LD junctions, controls LD nucleation and growth. However, how LD biogenesis is spatially and temporally coordinated remains elusive. Here, we show that the lipid transfer proteins ORP5 and ORP8 control LD biogenesis at mitochondria-associated ER membrane (MAM) subdomains, enriched in phosphatidic acid. We found that ORP5/8 regulates seipin recruitment to these MAM-LD contacts, and their loss impairs LD biogenesis. Importantly, the integrity of ER-mitochondria contact sites is crucial for ORP5/8 function in regulating seipin-mediated LD biogenesis. Our study uncovers an unprecedented ORP5/8 role in orchestrating LD biogenesis and maturation at MAMs and brings novel insights into the metabolic crosstalk between mitochondria, ER, and LDs at the membrane contact sites.

DOI: https://doi.org/10.1083/jcb.202112107
Front Aging Neurosci. 2022 ;14 858130

Transplantation of fecal microbiota from APP/PS1 mice and Alzheimer's disease patients enhanced endoplasmic reticulum stress in the cerebral cortex of wild-type mice.

Fang Wang, Yongzhe Gu, Chenhaoyi Xu, Kangshuai Du, Chence Zhao, Yanxin Zhao, Xueyuan Liu.

  Background and purpose: The gut-brain axis is bidirectional and the imbalance of the gut microbiota usually coexists with brain diseases, including Alzheimer's disease (AD). Accumulating evidence indicates that endoplasmic reticulum (ER) stress is a core lesion in AD and persistent ER stress promotes AD pathology and impairs cognition. However, whether the imbalance of the gut microbiota is involved in triggering the ER stress in the brain remains unknown.Materials and methods: In the present study, fecal microbiota transplantation (FMT) was performed with gut microbiota from AD patients and APP/PS1 mice, respectively, resulting in two mouse models with dysregulated gut microbiota. The ER stress marker protein levels in the cerebral cortex were assessed using western blotting. The composition of the gut microbiota was assessed using 16S rRNA sequencing.
Results: Excessive ER stress was induced in the cerebral cortex of mice after FMT. Elevated ER stress marker proteins (p-perk/perk, p-eIF2α/eIF2α) were observed, which were rescued by 3,3-dimethyl-1-butanol (DMB). Notably, DMB is a compound that significantly attenuates serum trimethylamine-N-oxide (TMAO), a metabolite of the gut microbiota widely reported to affect cognition.
Conclusion: The findings indicate that imbalance of the gut microbiota induces ER stress in the cerebral cortex, which may be mediated by TMAO.

Keywords:  Alzheimer’s disease; ER stress; FMT; TMAO; gut microbiota

DOI:  https://doi.org/10.3389/fnagi.2022.858130
Cell Death Dis. 2022 Aug 15. 13(8): 706

ER stress and UPR in Alzheimer's disease: mechanisms, pathogenesis, treatments.

Amir Ajoolabady, Dan Lindholm, Jun Ren, Domenico Pratico.

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by gradual loss of memory and cognitive function, which constitutes a heavy burden on the healthcare system globally. Current therapeutics to interfere with the underlying disease process in AD is still under development. Although many efforts have centered on the toxic forms of Aβ to effectively tackle AD, considering the unsatisfactory results so far it is vital to examine other targets and therapeutic approaches as well. The endoplasmic reticulum (ER) stress refers to the build-up of unfolded or misfolded proteins within the ER, thus, perturbing the ER and cellular homeostasis. Emerging evidence indicates that ER stress contributes to the onset and development of AD. A thorough elucidation of ER stress machinery in AD pathology may help to open up new therapeutic avenues in the management of this devastating condition to relieve the cognitive dementia symptoms. Herein, we aim at deciphering the unique role of ER stress in AD pathogenesis, reviewing key findings, and existing controversy in an attempt to summarize plausible therapeutic interventions in the management of AD pathophysiology.

DOI: https://doi.org/10.1038/s41419-022-05153-5
Immunometabolism (Cobham). 2022 Jul;4(3): e00007

PERK promotes immunosuppressive M2 macrophage phenotype by metabolic reprogramming and epigenetic modifications through the PERK-ATF4-PSAT1 axis.

Uday P Pratap, Ratna K Vadlamudi.

  The endoplasmic reticulum (ER) is a specialized organelle that participates in multiple cellular functions including protein folding, maturation, trafficking, and degradation to maintain homeostasis. However, hostile conditions in the tumor microenvironment (TME) disturb ER homeostasis. To overcome these conditions, cells activate ER stress response pathways, which are shown to augment the suppressive phenotypes of immune cells; however, the molecular mechanisms underpinning this process remain elusive. Here, we discuss a recent study by Raines et al, that suggests the role of the helper T-cell 2 (TH2) cytokine interleukin-4 (IL-4), and the TME in facilitating a protein kinase RNA-like ER kinase (PERK)-signaling cascade in macrophages, which promotes immunosuppressive M2 macrophage activation and proliferation. Further, the authors showed that PERK signaling promotes both mitochondrial respirations to fulfill cellular energy requirements and signaling through ATF4, which regulate phosphoserine aminotransferase 1 (PSAT1) activity to mediate the serine biosynthesis pathway. These results highlight a previously uncharacterized role for PERK in cellular metabolism and epigenetic modification in M2 macrophages, and thus offers a new therapeutic strategy for overcoming the immunosuppressive effects in the TME.

Keywords:  ER stress; M2 macrophage; endoplasmic reticulum; myeloid cell-derived suppressor cells; protein kinase RNA-like ER kinase; tumor-associated macrophages

DOI:  https://doi.org/10.1097/IN9.0000000000000007
Cell Biosci. 2022 Aug 14. 12(1): 129

Functions and mechanisms of protein disulfide isomerase family in cancer emergence.

Nisa Syakila A Rahman, Syazalina Zahari, Saiful Effendi Syafruddin, Mohd Firdaus-Raih, Teck Yew Low, M Aiman Mohtar.

The endoplasmic reticulum (ER) is a multi-layered organelle that is essential for the synthesis, folding, and structural maturation of almost one-third of the cellular proteome. It houses several resident proteins for these functions including the 21 members of the protein disulfide isomerase (PDI) family. The signature of proteins belonging to this family is the presence of the thioredoxin domain which mediates the formation, and rearrangement of disulfide bonds of substrate proteins in the ER. This process is crucial not only for the proper folding of ER substrates but also for maintaining a balanced ER proteostasis. The inclusion of new PDI members with a wide variety of structural determinants, size and enzymatic activity has brought additional epitomes of how PDI functions. Notably, some of them do not carry the thioredoxin domain and others have roles outside the ER. This also reflects that PDIs may have specialized functions and their functions are not limited within the ER. Large-scale expression datasets of human clinical samples have identified that the expression of PDI members is elevated in pathophysiological states like cancer. Subsequent functional interrogations using structural, molecular, cellular, and animal models suggest that some PDI members support the survival, progression, and metastasis of several cancer types. Herein, we review recent research advances on PDIs, vis-à-vis their expression, functions, and molecular mechanisms in supporting cancer growth with special emphasis on the anterior gradient (AGR) subfamily. Last, we posit the relevance and therapeutic strategies in targeting the PDIs in cancer.

DOI: https://doi.org/10.1186/s13578-022-00868-6
Front Plant Sci. 2022 ;13 923293

Subcellular trafficking and post-translational modification regulate PIN polarity in plants.

Shuyang Cheng, Yizhou Wang.

  Auxin regulates plant growth and tropism responses. As a phytohormone, auxin is transported between its synthesis sites and action sites. Most natural auxin moves between cells via a polar transport system that is mediated by PIN-FORMED (PIN) auxin exporters. The asymmetrically localized PINs usually determine the directionality of intercellular auxin flow. Different internal cues and external stimuli modulate PIN polar distribution and activity at multiple levels, including transcription, protein stability, subcellular trafficking, and post-translational modification, and thereby regulate auxin-distribution-dependent development. Thus, the different regulation levels of PIN polarity constitute a complex network. For example, the post-translational modification of PINs can affect the subcellular trafficking of PINs. In this review, we focus on subcellular trafficking and post-translational modification of PINs to summarize recent progress in understanding PIN polarity.

Keywords:  PINs; auxin transport; polarity; post-translational modification; subcellular trafficing

DOI:  https://doi.org/10.3389/fpls.2022.923293