bims-mecosi 2022-01-16 papers

bims-mecosi

Biomed News

on Membrane contact sites

Issue of 2022‒01‒16
eight papers selected by
Verena Kohler

Regulating peroxisome-ER contacts via the ACBD5-VAPB tether by FFAT motif phosphorylation and GSK3β.
Seipin localizes at endoplasmic-reticulum-mitochondria contact sites to control mitochondrial calcium import and metabolism in adipocytes.
Coordination of inter-organelle communication and lipid fluxes by OSBP-related proteins.
Nir1 constitutively localizes at ER-PM junctions and promotes Nir2 recruitment for PIP2 homeostasis.
Dysfunctional ER-mitochondrion coupling is associated with ER stress-induced apoptosis and neurological deficits in a rodent model of severe head injury.
Vps13-like proteins provide phosphatidylethanolamine for GPI anchor synthesis in the ER.
Disruption of ER-mitochondria tethering and signalling in C9orf72-associated amyotrophic lateral sclerosis and frontotemporal dementia.
Identification of endoplasmic reticulum formation mechanism by multi-parametric, quantitative super-resolution imaging.

J Cell Biol. 2022 Mar 07. pii: e202003143. [Epub ahead of print]221(3):

Regulating peroxisome-ER contacts via the ACBD5-VAPB tether by FFAT motif phosphorylation and GSK3β.

Suzan Kors, Christian Hacker, Chloe Bolton, Renate Maier, Lena Reimann, Emily J A Kitchener, Bettina Warscheid, Joseph L Costello, Michael Schrader.

Peroxisomes and the endoplasmic reticulum (ER) cooperate in cellular lipid metabolism. They form membrane contacts through interaction of the peroxisomal membrane protein ACBD5 (acyl-coenzyme A-binding domain protein 5) and the ER-resident protein VAPB (vesicle-associated membrane protein-associated protein B). ACBD5 binds to the major sperm protein domain of VAPB via its FFAT-like (two phenylalanines [FF] in an acidic tract) motif. However, molecular mechanisms, which regulate formation of these membrane contact sites, are unknown. Here, we reveal that peroxisome-ER associations via the ACBD5-VAPB tether are regulated by phosphorylation. We show that ACBD5-VAPB binding is phosphatase-sensitive and identify phosphorylation sites in the flanking regions and core of the FFAT-like motif, which alter interaction with VAPB-and thus peroxisome-ER contact sites-differently. Moreover, we demonstrate that GSK3β (glycogen synthase kinase-3 β) regulates this interaction. Our findings reveal for the first time a molecular mechanism for the regulation of peroxisome-ER contacts in mammalian cells and expand the current model of FFAT motifs and VAP interaction.

DOI: https://doi.org/10.1083/jcb.202003143
Cell Rep. 2022 Jan 11. pii: S2211-1247(21)01717-4. [Epub ahead of print]38(2): 110213

Seipin localizes at endoplasmic-reticulum-mitochondria contact sites to control mitochondrial calcium import and metabolism in adipocytes.

Yoann Combot, Veijo T Salo, Gilliane Chadeuf, Maarit Hölttä, Katharina Ven, Ilari Pulli, Simon Ducheix, Claire Pecqueur, Ophélie Renoult, Behnam Lak, Shiqian Li, Leena Karhinen, Ilya Belevich, Cedric Le May, Jennifer Rieusset, Soazig Le Lay, Mikael Croyal, Karim Si Tayeb, Helena Vihinen, Eija Jokitalo, Kid Törnquist, Corinne Vigouroux, Bertrand Cariou, Jocelyne Magré, Abdelhalim Larhlimi, Elina Ikonen, Xavier Prieur.

  Deficiency of the endoplasmic reticulum (ER) protein seipin results in generalized lipodystrophy by incompletely understood mechanisms. Here, we report mitochondrial abnormalities in seipin-deficient patient cells. A subset of seipin is enriched at ER-mitochondria contact sites (MAMs) in human and mouse cells and localizes in the vicinity of calcium regulators SERCA2, IP3R, and VDAC. Seipin association with MAM calcium regulators is stimulated by fasting-like stimuli, while seipin association with lipid droplets is promoted by lipid loading. Acute seipin removal does not alter ER calcium stores but leads to defective mitochondrial calcium import accompanied by a widespread reduction in Krebs cycle metabolites and ATP levels. In mice, inducible seipin deletion leads to mitochondrial dysfunctions preceding the development of metabolic complications. Together, these data suggest that seipin controls mitochondrial energy metabolism by regulating mitochondrial calcium influx at MAMs. In seipin-deficient adipose tissue, reduced ATP production compromises adipocyte properties, contributing to lipodystrophy pathogenesis.

Keywords:  ATP production; Adipocyte; Calcium handling; ER-LD contact sites; Krebs cycle metabolites; MAMs; Mitochondria dysfunction; lipid droplet; lipodystrophy; seipin

DOI:  https://doi.org/10.1016/j.celrep.2021.110213
Prog Lipid Res. 2022 Jan 06. pii: S0163-7827(22)00001-7. [Epub ahead of print] 101146

Coordination of inter-organelle communication and lipid fluxes by OSBP-related proteins.

Amita Arora, Juuso H Taskinen, Vesa M Olkkonen.

  Oxysterol-binding protein (OSBP) and OSBP-related proteins (ORPs) constitute one of the largest families of lipid-binding/transfer proteins (LTPs) in eukaryotes. The current view is that many of them mediate inter-organelle lipid transfer over membrane contact sites (MCS). The transfer occurs in several cases in a 'counter-current' fashion: A lipid such as cholesterol or phosphatidylserine (PS) is transferred against its concentration gradient driven by transport of a phosphoinositide in the opposite direction. In this way ORPs are envisioned to maintain the distinct organelle lipid compositions, with impacts on multiple organelle functions. However, the functions of ORPs extend beyond lipid homeostasis to regulation of processes such as cell survival, proliferation and migration. Important expanding areas of mammalian ORP research include their roles in viral and bacterial infections, cancers, and neuronal function. The yeast OSBP homologue (Osh) proteins execute multifaceted functions in sterol and glycerophospholipid homeostasis, post-Golgi vesicle transport, phosphatidylinositol-4-phosphate, sphingolipid and target of rapamycin (TOR) signalling, and cell cycle control. These observations identify ORPs as lipid transporters and coordinators of signals with an unforeseen variety of cellular processes. Understanding their activities not only enlightens the biology of the living cell but also allows their employment as targets of new therapeutic approaches for disease.

Keywords:  Cell signalling; Lipid metabolism; Lipid transport; Membrane contact site; ORP; OSBPL

DOI:  https://doi.org/10.1016/j.plipres.2022.101146
Mol Biol Cell. 2022 Jan 12. mbcE21070356

Nir1 constitutively localizes at ER-PM junctions and promotes Nir2 recruitment for PIP2 homeostasis.

Carlo Giovanni Quintanilla, Wan-Ru Lee, Jen Liou.

Homeostatic regulation of plasma membrane (PM) phosphatidylinositol 4,5-bisphosphate (PIP2) in receptor-stimulated cells is mediated by the lipid transfer protein Nir2. Nir2 is dynamically recruited to endoplasmic reticulum-plasma membrane (ER-PM) junctions to facilitate replenishment of PM PIP2 hydrolyzed during receptor-mediated signaling. However, our knowledge regarding the activation and sustainment of Nir2-mediated replenishment of PM PIP2 is limited. Here, we describe the functions of Nir1 as a positive regulator of Nir2 and PIP2 homeostasis. In contrast to the family proteins Nir2 and Nir3, Nir1 constitutively localizes at ER-PM junctions. Nir1 potentiates Nir2 targeting to ER-PM junctions during receptor-mediated signaling and is required for efficient PM PIP2 replenishment. Live-cell imaging and biochemical analysis reveal that Nir1 interacts with Nir2 via a region between the FFAT motif and the DDHD domain. Combined, results from this study identify Nir1 as an ER-PM junction localized protein that promotes Nir2 recruitment for PIP2 homeostasis.

DOI: https://doi.org/10.1091/mbc.E21-07-0356
J Neurotrauma. 2022 Jan 12.

Dysfunctional ER-mitochondrion coupling is associated with ER stress-induced apoptosis and neurological deficits in a rodent model of severe head injury.

Xin Chen, Liang Mi, Gang Gu, Xiangliang Gao, Mingming Shi, Yan Chai, Fanglian Chen, Weidong Yang, Jian-Ning Zhang.

  Cellular homeostasis requires critical communications between the endoplasmic reticulum (ER) and mitochondria to maintain the viability of cells. This communication is mediated and maintained by the mitochondria-associated membranes (MAMs) and may be disrupted during acute traumatic brain injury (TBI), leading to structural and functional damages of neurons and supporting cells. To test this hypothesis, we subjected male C57BL/6 mice to severe TBI (sTBI) using a controlled cortical impact (CCI) device. We analyzed the physical ER-mitochondrion contacts in the perilesional cortex using transmission electron microscopy, western blot, and immunofluorescence. We specifically measured changes in the production of reactive oxygen species (ROS) in mitochondria, the unfolded protein response (UPR), the neuroinflammatory response, and ER stress-mediated apoptosis in the traumatic injured cerebral tissue. A modified neurological severity score (mNSS) was used to evaluate neurological function in the sTBI mice. We found that sTBI induced significant reorganizations of MEMs in the cerebral cortex within the first 24 hr post-injury. This ER-mitochondrion coupling was enhanced, reaching its peak level at 6 hrs post-sTBI. This enhanced coupling correlated closely with increases in the expression of the Ca2+ regulatory proteins (IP3R1, VDAC1, GRP75, Sigma-1R), production of ROS, degree of ER stress, levels of UPR, and release of proinflammatory cytokines. Furthermore, the neurological function of sTBI mice was significantly improved by silencing the gene for the ER-mitochondrion tethering factor PACS2, restoring the IP3R1-GRP75-VDAC1 axis of Ca2+ regulation, alleviating mitochondria-derived oxidative stress, suppressing inflammatory response through the PERK/eIF2α/ATF4/CHOP pathway, and inhibiting ER stress and associated apoptosis. These results indicate that dysfunctional ER-mitochondrion coupling might be primarily involved in the neuronal apoptosis and neurological deficits, and modulating the ER-mitochondrion crosstalk might be a novel therapeutic strategy for sTBI.

Keywords:  Apoptosis; MITOCHONDRIA; OXIDATIVE STRESS; TRAUMATIC BRAIN INJURY

DOI:  https://doi.org/10.1089/neu.2021.0347
J Cell Biol. 2022 Mar 07. pii: e202111095. [Epub ahead of print]221(3):

Vps13-like proteins provide phosphatidylethanolamine for GPI anchor synthesis in the ER.

Alexandre Toulmay, Fawn B Whittle, Jerry Yang, Xiaofei Bai, Jessica Diarra, Subhrajit Banerjee, Tim P Levine, Andy Golden, William A Prinz.

Glycosylphosphatidylinositol (GPI) is a glycolipid membrane anchor found on surface proteins in all eukaryotes. It is synthesized in the ER membrane. Each GPI anchor requires three molecules of ethanolamine phosphate (P-Etn), which are derived from phosphatidylethanolamine (PE). We found that efficient GPI anchor synthesis in Saccharomyces cerevisiae requires Csf1; cells lacking Csf1 accumulate GPI precursors lacking P-Etn. Structure predictions suggest Csf1 is a tube-forming lipid transport protein like Vps13. Csf1 is found at contact sites between the ER and other organelles. It interacts with the ER protein Mcd4, an enzyme that adds P-Etn to nascent GPI anchors, suggesting Csf1 channels PE to Mcd4 in the ER at contact sites to support GPI anchor biosynthesis. CSF1 has orthologues in Caenorhabditis elegans (lpd-3) and humans (KIAA1109/TWEEK); mutations in KIAA1109 cause the autosomal recessive neurodevelopmental disorder Alkuraya-Kučinskas syndrome. Knockout of lpd-3 and knockdown of KIAA1109 reduced GPI-anchored proteins on the surface of cells, suggesting Csf1 orthologues in human cells support GPI anchor biosynthesis.

DOI: https://doi.org/10.1083/jcb.202111095
Aging Cell. 2022 Jan 13. e13549

Disruption of ER-mitochondria tethering and signalling in C9orf72-associated amyotrophic lateral sclerosis and frontotemporal dementia.

Patricia Gomez-Suaga, Gábor M Mórotz, Andrea Markovinovic, Sandra M Martín-Guerrero, Elisavet Preza, Natalia Arias, Keith Mayl, Afra Aabdien, Vesela Gesheva, Agnes Nishimura, Ambra Annibali, Younbok Lee, Jacqueline C Mitchell, Selina Wray, Christopher Shaw, Wendy Noble, Christopher C J Miller.

  Hexanucleotide repeat expansions in C9orf72 are the most common cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The mechanisms by which the expansions cause disease are not properly understood but a favoured route involves its translation into dipeptide repeat (DPR) polypeptides, some of which are neurotoxic. However, the precise targets for mutant C9orf72 and DPR toxicity are not fully clear, and damage to several neuronal functions has been described. Many of these functions are regulated by signalling between the endoplasmic reticulum (ER) and mitochondria. ER-mitochondria signalling requires close physical contacts between the two organelles that are mediated by the VAPB-PTPIP51 'tethering' proteins. Here, we show that ER-mitochondria signalling and the VAPB-PTPIP51 tethers are disrupted in neurons derived from induced pluripotent stem (iPS) cells from patients carrying ALS/FTD pathogenic C9orf72 expansions and in affected neurons in mutant C9orf72 transgenic mice. In these mice, disruption of the VAPB-PTPIP51 tethers occurs prior to disease onset suggesting that it contributes to the pathogenic process. We also show that neurotoxic DPRs disrupt the VAPB-PTPIP51 interaction and ER-mitochondria contacts and that this may involve activation of glycogen synthase kinases-3β (GSK3β), a known negative regulator of VAPB-PTPIP51 binding. Finally, we show that these DPRs disrupt delivery of Ca2+ from ER stores to mitochondria, which is a primary function of the VAPB-PTPIP51 tethers. This delivery regulates a number of key neuronal functions that are damaged in ALS/FTD including bioenergetics, autophagy and synaptic function. Our findings reveal a new molecular target for mutant C9orf72-mediated toxicity.

Keywords:   C9orf72 ; GSK3β; PTPIP51; VAPB; amyotrophic lateral sclerosis; endoplasmic reticulum; frontotemporal dementia; mitochondria

DOI:  https://doi.org/10.1111/acel.13549
Opt Lett. 2022 Jan 15. 47(2): 357-360

Identification of endoplasmic reticulum formation mechanism by multi-parametric, quantitative super-resolution imaging.

Shuhao Qian, Jia Meng, Wenjie Liu, Chuncheng Wang, Rushan Jiang, Lu Yang, Xu Liu, Cuifang Kuang, Zhihua Ding, Zhiyi Liu.

The endoplasmic reticulum (ER) is a highly dynamic membrane-bound organelle in eukaryotic cells which spreads throughout the whole cell and contacts and interacts with almost all organelles, yet quantitative approaches to assess ER reorganization are lacking. Herein we propose a multi-parametric, quantitative method combining pixel-wise orientation and waviness features and apply it to the time-dependent images of co-labeled ER and microtubule (MT) from U2OS cells acquired from two-dimensional structured illumination microscopy (2D SIM). Analysis results demonstrate that these morphological features are sensitive to ER reshaping and a combined use of them is a potential biomarker for ER formation. A new, to the best of our knowledge, mechanism of MT-associated ER formation, termed hooking, is identified based on distinct organizational alterations caused by interaction between ER and MT which are different from those of the other three mechanisms already known, validated by 100% discrimination accuracy in classifying four MT-associated ER formation mechanisms.

DOI: https://doi.org/10.1364/OL.445744