bims-mecosi 2023-05-21 papers

bims-mecosi

Biomed News

on Membrane contact sites

Issue of 2023–05–21
nine papers selected by
Verena Kohler, University of Graz

The Effects of PP2A Disruption on ER-Mitochondria Contact and Mitochondrial Functions in Neuronal-like Cells.
The C10orf76-PI4KB axis orchestrates CERT-mediated ceramide trafficking to the distal Golgi.
Partial Inhibition of Complex I Restores Mitochondrial Morphology and Mitochondria-ER Communication in Hippocampus of APP/PS1 Mice.
The spatial expression of mTORC2-AKT-IP3R signal pathway in mitochondrial combination of endoplasmic reticulum of maternal fetal interface trophoblast in intrahepatic cholestasis of pregnancy.
Giant worm-shaped ESCRT scaffolds surround actin-independent integrin clusters.
DNA Methylation-Mediated Mfn2 Gene Regulation in the Brain: A Role in Brain Trauma-Induced Mitochondrial Dysfunction and Memory Deficits.
Anaphylatoxin C5a receptor signaling induces mitochondrial fusion and sensitizes retina pigment epithelial cells to oxidative stress.
Mitochondrial Ca2+ signaling and Alzheimer's disease: Too much or too little?
Mitochondria are midfield players in steroid synthesis.

Biomedicines. 2023 Mar 26. pii: 1011. [Epub ahead of print]11(4):

The Effects of PP2A Disruption on ER-Mitochondria Contact and Mitochondrial Functions in Neuronal-like Cells.

Phaewa Chaiwijit, Kwanchanok Uppakara, Nithi Asavapanumas, Witchuda Saengsawang.

  Mitochondria-associated membranes (MAMs) regulate several cellular processes, including calcium homeostasis and mitochondrial function, and dynamics. While MAMs are upregulated in Alzheimer's disease (AD), the mechanisms underlying this increase remain unknown. A possible mechanism may include dysregulation of protein phosphatase 2A (PP2A), which is reduced in the AD brain. Furthermore, PP2A has been previously reported to modulate MAM formation in hepatocytes. However, it is unknown whether PP2A and MAMs are linked in neuronal cells. Here, to test the correlation between PP2A and MAMs, we inhibited the activity of PP2A to mimic its low levels in AD brains and observed MAM formation, function, and dynamics. MAMs were significantly increased after PP2A inhibition, which correlated with elevated mitochondrial Ca2+ influx and disrupted mitochondrial membrane potential and mitochondrial fission. This study highlights the essential role PP2A plays in regulating MAM formation and mitochondrial function and dynamics for the first time in neuronal-like cells.

Keywords:  Alzheimer’s disease; ER-mitochondria contacts; MAMs; PP2A; Tau; calcium; mitochondrial dynamics

DOI:  https://doi.org/10.3390/biomedicines11041011
J Cell Biol. 2023 Jul 03. pii: e202111069. [Epub ahead of print]222(7):

The C10orf76-PI4KB axis orchestrates CERT-mediated ceramide trafficking to the distal Golgi.

Aya Mizuike, Shota Sakai, Kaoru Katoh, Toshiyuki Yamaji, Kentaro Hanada.

Phosphatidylinositol 4-monophosphate [PtdIns(4)P] is a precursor for various phosphoinositides but also a membrane-embedded component crucial for membrane contact sites (MCSs). Several lipid transfer proteins are recruited to MCSs by recognizing PtdIns(4)P; however, it remains poorly elucidated how the production of PtdIns(4)P for lipid transport at MCSs is regulated. Following human genome-wide screening, we discovered that the PtdIns(4)P-related genes PI4KB, ACBD3, and C10orf76 are involved in endoplasmic reticulum-to-Golgi trafficking of ceramide by the ceramide transport protein CERT. CERT preferentially utilizes PtdIns(4)P generated by PI4KB recruited to the Golgi by C10orf76 rather than by ACBD3. Super-resolution microscopy observation revealed that C10orf76 predominantly localizes at distal Golgi regions, where sphingomyelin (SM) synthesis primarily occurs, while the majority of ACBD3 localizes at more proximal regions. This study provides a proof-of-concept that distinct pools of PtdIns(4)P are generated in different subregions, even within the same organelle, to facilitate interorganelle metabolic channeling for the ceramide-to-SM conversion.

DOI: https://doi.org/10.1083/jcb.202111069
Cells. 2023 04 08. pii: 1111. [Epub ahead of print]12(8):

Partial Inhibition of Complex I Restores Mitochondrial Morphology and Mitochondria-ER Communication in Hippocampus of APP/PS1 Mice.

Jessica Panes, Thi Kim Oanh Nguyen, Huanyao Gao, Trace A Christensen, Andrea Stojakovic, Sergey Trushin, Jeffrey L Salisbury, Jorge Fuentealba, Eugenia Trushina.

  Alzheimer's disease (AD) has no cure. Earlier, we showed that partial inhibition of mitochondrial complex I (MCI) with the small molecule CP2 induces an adaptive stress response, activating multiple neuroprotective mechanisms. Chronic treatment reduced inflammation, Aβ and pTau accumulation, improved synaptic and mitochondrial functions, and blocked neurodegeneration in symptomatic APP/PS1 mice, a translational model of AD. Here, using serial block-face scanning electron microscopy (SBFSEM) and three-dimensional (3D) EM reconstructions combined with Western blot analysis and next-generation RNA sequencing, we demonstrate that CP2 treatment also restores mitochondrial morphology and mitochondria-endoplasmic reticulum (ER) communication, reducing ER and unfolded protein response (UPR) stress in the APP/PS1 mouse brain. Using 3D EM volume reconstructions, we show that in the hippocampus of APP/PS1 mice, dendritic mitochondria primarily exist as mitochondria-on-a-string (MOAS). Compared to other morphological phenotypes, MOAS have extensive interaction with the ER membranes, forming multiple mitochondria-ER contact sites (MERCS) known to facilitate abnormal lipid and calcium homeostasis, accumulation of Aβ and pTau, abnormal mitochondrial dynamics, and apoptosis. CP2 treatment reduced MOAS formation, consistent with improved energy homeostasis in the brain, with concomitant reductions in MERCS, ER/UPR stress, and improved lipid homeostasis. These data provide novel information on the MOAS-ER interaction in AD and additional support for the further development of partial MCI inhibitors as a disease-modifying strategy for AD.

Keywords:  Alzheimer’s disease (AD); endoplasmic reticulum (ER); mitochondria; serial block-face scanning electron microscopy (SBFSEM); small molecule mitochondria targeted therapeutics; three-dimensional electron microscopy (3DEM)

DOI:  https://doi.org/10.3390/cells12081111
J Perinat Med. 2023 Apr 28.

The spatial expression of mTORC2-AKT-IP3R signal pathway in mitochondrial combination of endoplasmic reticulum of maternal fetal interface trophoblast in intrahepatic cholestasis of pregnancy.

Yaqian Li, Daijuan Chen, Jinfeng Xu, Xiaodong Wang, Fan Zhou.

   OBJECTIVES: Intrahepatic cholestasis of pregnancy (ICP) is complicated by adverse fetal outcomes and even fetal death, the mechanism remains unclear. This study aims at evaluating the differential expression of mTORC2-AKT-IP3R signaling pathway, which accurately regulate Ca2+ transfer across mitochondria-associated membranes (MAMs) and determine the stress intensity experienced by endoplasmic reticulum (ER) and mitochondria, in patients diagnosed with ICP.
METHODS: We combined western blot analysis and placental immunofluorescence co-localization detection to assess the expression and co-localization of the mTORC2-AKT-IP3R signaling pathway in severe (maternal total bile acid (TBA) levels ≥40 μmol/L) and mild (maternal TBA 10-40 μmol/L) ICP.
RESULTS: Compared with the control and mild ICP groups, phosphorylated protein kinase B (p-AKT) levels were significantly upregulated in the severe ICP group. Placental Rictor levels were lower in the mild ICP group than in the control group and were further downregulated in the severe ICP group. IP3R3 and p-IP3R3 levels were lower in placentas in the severe ICP group than in those in the mild ICP and control groups. Moreover, the co-localization of IP3R3 and p-AKT in patients in the mild and severe ICP groups was significantly elevated compared with that in patients in the control group.
CONCLUSIONS: In patients with severe ICP, limited expression of Rictor and elevated p-AKT levels would suppress IP3R3/p-IP3R3 levels in MAMs. This inhibition might influence the transportation of Ca2+ from the ER to the mitochondria, thus weaken the stress adaptation associated with MAMs. Our results reveal the possible pathophysiological mechanism of adverse fetal outcomes in ICP.

Keywords:  bile acid; calcium; intrahepatic cholestasis of pregnancy; mitochondria-associated membranes; placenta; stress

DOI:  https://doi.org/10.1515/jpm-2022-0570
J Cell Biol. 2023 Jul 03. pii: e202205130. [Epub ahead of print]222(7):

Giant worm-shaped ESCRT scaffolds surround actin-independent integrin clusters.

Femmy C Stempels, Muwei Jiang, Harry M Warner, Magda-Lena Moser, Maaike H Janssens, Sjors Maassen, Iris H Nelen, Rinse de Boer, William F Jiemy, David Knight, Julian Selley, Ronan O'Cualain, Maksim V Baranov, Thomas C Q Burgers, Roberto Sansevrino, Dragomir Milovanovic, Peter Heeringa, Matthew C Jones, Rifka Vlijm, Martin Ter Beest, Geert van den Bogaart.

Endosomal Sorting Complex Required for Transport (ESCRT) proteins can be transiently recruited to the plasma membrane for membrane repair and formation of extracellular vesicles. Here, we discovered micrometer-sized worm-shaped ESCRT structures that stably persist for multiple hours at the plasma membrane of macrophages, dendritic cells, and fibroblasts. These structures surround clusters of integrins and known cargoes of extracellular vesicles. The ESCRT structures are tightly connected to the cellular support and are left behind by the cells together with surrounding patches of membrane. The phospholipid composition is altered at the position of the ESCRT structures, and the actin cytoskeleton is locally degraded, which are hallmarks of membrane damage and extracellular vesicle formation. Disruption of actin polymerization increased the formation of the ESCRT structures and cell adhesion. The ESCRT structures were also present at plasma membrane contact sites with membrane-disrupting silica crystals. We propose that the ESCRT proteins are recruited to adhesion-induced membrane tears to induce extracellular shedding of the damaged membrane.

DOI: https://doi.org/10.1083/jcb.202205130
Cell Mol Neurobiol. 2023 May 16.

DNA Methylation-Mediated Mfn2 Gene Regulation in the Brain: A Role in Brain Trauma-Induced Mitochondrial Dysfunction and Memory Deficits.

Prakash G Kulkarni, Nagalakshmi Balasubramanian, Ritika Manjrekar, Tanushree Banerjee, Amul Sakharkar.

  Repeated mild traumatic brain injuries (rMTBI) affect mitochondrial homeostasis in the brain. However, mechanisms of long-lasting neurobehavioral effects of rMTBI are largely unknown. Mitofusin 2 (Mfn2) is a critical component of tethering complexes in mitochondria-associated membranes (MAMs) and thereby plays a pivotal role in mitochondrial functions. Herein, we investigated the implications of DNA methylation in the Mfn2 gene regulation, and its consequences on mitochondrial dysfunction in the hippocampus after rMTBI. rMTBI dramatically reduced the mitochondrial mass, which was concomitant with decrease in Mfn2 mRNA and protein levels. DNA hypermethylation at the Mfn2 gene promoter was observed post 30 days of rMTBI. The treatment of 5-Azacytidine, a pan DNA methyltransferase inhibitor, normalized DNA methylation levels at Mfn2 promoter, which further resulted into restoration of Mfn2 function. The normalization of Mfn2 function was well correlated with recovery in memory deficits in rMTBI-exposed rats. Since, glutamate excitotoxicity serves as a primary insult after TBI, we employed in vitro model of glutamate excitotoxicity in human neuronal cell line SH-SY5Y to investigate the causal epigenetic mechanisms of Mfn2 gene regulation. The glutamate excitotoxicity reduced Mfn2 levels via DNA hypermethylation at Mfn2 promoter. Loss of Mfn2 caused significant surge in cellular and mitochondrial ROS levels with lowered mitochondrial membrane potential in cultured SH-SY5Y cells. Like rMTBI, these consequences of glutamate excitotoxicity were also prevented by 5-AzaC pre-treatment. Therefore, DNA methylation serves as a vital epigenetic mechanism involved in Mfn2 expression in the brain; and this Mfn2 gene regulation may play a pivotal role in rMTBI-induced persistent cognitive deficits. Closed head weight drop injury method was employed to induce repeated mild traumatic brain (rMTBI) in jury in adult, male Wistar rats. rMTBI causes hyper DNA methylation at the Mfn2 promoter and lowers the Mfn2 expression triggering mitochondrial dysfunction. However, the treatment of 5-azacytidine normalizes DNA methylation at the Mfn2 promoter and restores mitochondrial function.

Keywords:  DNA methylation; Glutamate excitotoxicity; Mitochondrial dysfunction; Mitofusin-2; Repeated mild traumatic brain injury

DOI:  https://doi.org/10.1007/s10571-023-01358-0
Biochim Biophys Acta Gen Subj. 2023 May 13. pii: S0304-4165(23)00072-7. [Epub ahead of print] 130374

Anaphylatoxin C5a receptor signaling induces mitochondrial fusion and sensitizes retina pigment epithelial cells to oxidative stress.

Masaaki Ishii, Bärbel Rohrer.

  Mitochondrial dynamics is a morphological balance between fragmented and elongated shapes, reflecting mitochondrial metabolic status, cellular damage, and mitochondrial dysfunction. The anaphylatoxin C5a derived from complement component 5 cleavage, enhances cellular responses involved in pathological stimulation, innate immune responses, and host defense. However, the specific response of C5a and its receptor, C5a receptor (C5aR), in mitochondria is unclear. Here, we tested whether the C5a/C5aR signaling axis affects mitochondrial morphology in human-derived retinal pigment epithelial cell monolayers (ARPE-19). C5aR activation with the C5a polypeptide-induced mitochondrial elongation. In contrast, oxidatively stressed cells (H2O2) responded to C5a with an enhancement of mitochondrial fragmentation and an increase in the number of pyknotic nuclei. C5a/C5aR signaling increased the expression of mitochondrial fusion-related protein, mitofusin-1 (MFN1) and - 2 (MFN2), as well as enhanced optic atrophy-1 (Opa1) cleavage, which are required for mitochondrial fusion events, whereas the mitochondrial fission protein, dynamin-related protein-1 (Drp1), and mitogen-activated protein kinase (MAPK)-dependent extracellular signal-regulated protein kinase (Erk1/2) phosphorylation were not affected. Moreover, C5aR activation increased the frequency of endoplasmic reticulum (ER)-mitochondria contacts. Finally, oxidative stress induced in a single cell within an RPE monolayer (488 nm blue laser spot stimulation) induced a bystander effect of mitochondrial fragmentation in adjacent surrounding cells only in C5a-treated monolayers. These results suggest that C5a/C5aR signaling produced an intermediate state, characterized by increased mitochondrial fusion and ER-mitochondrial contacts, that sensitizes cells to oxidative stress, leading to mitochondrial fragmentation and cell death.

Keywords:  Anaphylatoxin; ER-mitochondria contact; G-protein coupled receptor; Mitochondrial dynamics

DOI:  https://doi.org/10.1016/j.bbagen.2023.130374
Cell Calcium. 2023 May 11. pii: S0143-4160(23)00069-6. [Epub ahead of print]113 102757

Mitochondrial Ca2+ signaling and Alzheimer's disease: Too much or too little?

Paloma Garcia-Casas, Michela Rossini, Riccardo Filadi, Paola Pizzo.

  Alzheimer's disease (AD) is a neurodegenerative disease, caused by poorly known pathogenic mechanisms and aggravated by delayed therapeutic intervention, that still lacks an effective cure. However, it is clear that some important neurophysiological processes are altered years before the onset of clinical symptoms, offering the possibility of identifying biological targets useful for implementation of new therapies. Of note, evidence has been provided suggesting that mitochondria, pivotal organelles in sustaining neuronal energy demand and modulating synaptic activity, are dysfunctional in AD samples. In particular, alterations in mitochondrial Ca2+ signaling have been proposed as causal events for neurodegeneration, although the exact outcomes and molecular mechanisms of these defects, as well as their longitudinal progression, are not always clear. Here, we discuss the importance of a correct mitochondrial Ca2+ handling for neuronal physiology and summarize the latest findings on dysfunctional mitochondrial Ca2+ pathways in AD, analysing possible consequences contributing to the neurodegeneration that characterizes the disease.

Keywords:  Alzheimer's disease; ER-mitochondria contacts; MCU; Mitochondrial calcium signaling; NCLX; Presenilin

DOI:  https://doi.org/10.1016/j.ceca.2023.102757
Int J Biochem Cell Biol. 2023 May 17. pii: S1357-2725(23)00070-5. [Epub ahead of print] 106431

Mitochondria are midfield players in steroid synthesis.

Philipp Melchinger, Bruna Martins Garcia.

  Steroids are important membrane components and signaling metabolites and thus are required for cellular homeostasis. All mammalian cells retain the ability to uptake and synthesize steroids. Dysregulation of steroid levels leads to profound effects on cellular function and organismal health. Hence it comes as no surprise that steroid synthesis is tightly regulated. It is well established that the main site for steroid synthesis and regulation is the endoplasmic reticulum. However, mitochondria are essential for: (1) cholesterol production (the precursor of all steroids) by exporting citrate and; (2) the products of steroidogenesis (such as mineralocorticoids and glucocorticoids). In this review, we describe the midfield player role of mitochondria in steroid synthesis and bring the idea of mitochondria actively participating in steroid synthesis regulation. A better understanding of the mitochondrial regulatory roles in steroid synthesis would open new avenues to targeted approaches aiming to control steroid levels.

Keywords:  Cholesterol synthesis; Mitochondria-ER contact; Steroid hormones

DOI:  https://doi.org/10.1016/j.biocel.2023.106431