bims-mecosi 2023-05-28 papers

bims-mecosi

Biomed News

on Membrane contact sites

Issue of 2023–05–28
ten papers selected by
Verena Kohler, University of Graz

Pathogen vacuole membrane contact sites - close encounters of the fifth kind.
Above the legal limit: Alcohol brings ER and mitochondria too close together.
Coronaviral ORF6 protein mediates inter-organelle contacts and modulates host cell lipid flux for virus production.
Single-cell transcriptional profiling of hearts during cardiac hypertrophy reveals the role of MAMs in cardiomyocyte subtype switching.
DsbA-L alleviated tubular injury in diabetic nephropathy via activating mitophagy through maintain MAM integrity.
Mitochondrial Connexins and Mitochondrial Contact Sites with Gap Junction Structure.
AMPK-endoplasmic reticulum stress axis contributes to lipopolysaccharide-caused mitochondrial dysfunction by regulating mitochondria-associated membrane function in bovine hepatocytes.
Interplay between calcium and endoplasmic reticulum stress.
Metamorphic proteins at the basis of human autophagy initiation and lipid transfer.
Rebalancing Cardiac Structure and Function With Synthetic Mitochondria-Endoplasmic Reticulum Tethers.

Microlife. 2023 ;4 uqad018

Pathogen vacuole membrane contact sites - close encounters of the fifth kind.

Simone Vormittag, Rachel J Ende, Isabelle Derré, Hubert Hilbi.

  Vesicular trafficking and membrane fusion are well-characterized, versatile, and sophisticated means of 'long range' intracellular protein and lipid delivery. Membrane contact sites (MCS) have been studied in far less detail, but are crucial for 'short range' (10-30 nm) communication between organelles, as well as between pathogen vacuoles and organelles. MCS are specialized in the non-vesicular trafficking of small molecules such as calcium and lipids. Pivotal MCS components important for lipid transfer are the VAP receptor/tether protein, oxysterol binding proteins (OSBPs), the ceramide transport protein CERT, the phosphoinositide phosphatase Sac1, and the lipid phosphatidylinositol 4-phosphate (PtdIns(4)P). In this review, we discuss how these MCS components are subverted by bacterial pathogens and their secreted effector proteins to promote intracellular survival and replication.

Keywords:  Chlamydia; Coxiella; Dictyostelium discoideum; FFAT motif; Legionella; Legionnaires’ disease; Sac1 phosphoinositide phosphatase; Salmonella; VAP; endoplasmic reticulum; lipid transfer proteins; membrane contact site; oxysterol binding proteins; pathogen vacuole; phosphoinositide

DOI:  https://doi.org/10.1093/femsml/uqad018
Cell Calcium. 2023 May 22. pii: S0143-4160(23)00075-1. [Epub ahead of print]113 102763

Above the legal limit: Alcohol brings ER and mitochondria too close together.

Mateus T Guerra, Michael H Nathanson.

Mitochondria-associated membranes (MAMs) are signaling domains formed at points of contact between the endoplasmic reticulum and mitochondria that are essential for mitochondrial Ca2+ signaling, energy metabolism and cell survival. Thoudam et al. now show that MAMs are dynamically regulated by pyruvate dehydrogenase kinase 4 in alcohol-associate liver disease, adding one more piece to the ever more complex puzzle of ER-mitochondria interactions in health and disease.

DOI: https://doi.org/10.1016/j.ceca.2023.102763
EMBO J. 2023 May 23. e112542

Coronaviral ORF6 protein mediates inter-organelle contacts and modulates host cell lipid flux for virus production.

Mengzhen Yue, Bing Hu, Jiajia Li, Ruifeng Chen, Zhen Yuan, Hurong Xiao, Haishuang Chang, Yaming Jiu, Kun Cai, Binbin Ding.

  Lipid droplets (LDs) form inter-organelle contacts with the endoplasmic reticulum (ER) that promote their biogenesis, while LD contacts with mitochondria enhance β-oxidation of contained fatty acids. Viruses have been shown to take advantage of lipid droplets to promote viral production, but it remains unclear whether they also modulate the interactions between LDs and other organelles. Here, we showed that coronavirus ORF6 protein targets LDs and is localized to the mitochondria-LD and ER-LD contact sites, where it regulates LD biogenesis and lipolysis. At the molecular level, we find that ORF6 inserts into the LD lipid monolayer via its two amphipathic helices. ORF6 further interacts with ER membrane proteins BAP31 and USE1 to mediate ER-LDs contact formation. Additionally, ORF6 interacts with the SAM complex in the mitochondrial outer membrane to link mitochondria to LDs. In doing so, ORF6 promotes cellular lipolysis and LD biogenesis to reprogram host cell lipid flux and facilitate viral production.

Keywords:  ORF6; endoplasmic reticulum; lipid droplets; mitochondria; organelle interaction

DOI:  https://doi.org/10.15252/embj.2022112542
Sci Rep. 2023 May 23. 13(1): 8339

Single-cell transcriptional profiling of hearts during cardiac hypertrophy reveals the role of MAMs in cardiomyocyte subtype switching.

Yi Luan, Guangyu Guo, Ying Luan, Yang Yang, Ruixia Yuan.

Pathological cardiac hypertrophy is the main predecessor of heart failure. Its pathology is sophisticated, and its progression is associated with multiple cellular processes. To explore new therapeutic approaches, more precise examination of cardiomyocyte subtypes and involved biological processes is required in response to hypertrophic stimuli. Mitochondria and the endoplasmic reticulum (ER) are two crucial organelles associated with the progression of cardiac hypertrophy and are connected through junctions known as mitochondria-associated endoplasmic reticulum membranes (MAMs). Although MAM genes are altered in cardiac hypertrophy, the importance of MAMs in cardiac hypertrophy and the expression pattern of MAMs in certain cardiac cell types require a comprehensive analysis. In this study, we analyzed the temporal expression of MAM proteins in the process of cardiac hypertrophy and observed that MAM-related proteins preferentially accumulated in cardiomyocytes at the initial stage of cardiac hypertrophy and underwent a gradual decline, which was synchronized with the proportion of two cardiomyocyte subtypes (CM2 and CM3). Meanwhile, these subtypes went through a functional switch during cardiac hypertrophy. Trajectory analysis suggested that there was a differentiation trajectory of cardiomyocyte subtypes from high to low MAM protein expression. Distinct regulon modules across different cardiomyocyte cell types were revealed by transcriptional regulatory network analysis. Furthermore, scWGCNA revealed that MAM-related genes were clustered into a module that correlated with diabetic cardiomyopathy. Altogether, we identified cardiomyocyte subtype transformation and the potential critical transcription factors involved, which may serve as therapeutic targets in combating cardiac hypertrophy.

DOI: https://doi.org/10.1038/s41598-023-35464-2
Clin Sci (Lond). 2023 May 25. pii: CS20220787. [Epub ahead of print]

DsbA-L alleviated tubular injury in diabetic nephropathy via activating mitophagy through maintain MAM integrity.

Lin Sun, Ming Yang, Qin Zhang, Shilu Luo, Yachun Han, Hao Zhao, Na Jiang, Yan Liu, Li Li, Chenrui Li, Chongbin Liu, Liyu He, Xuejing Zhu, Yu Liu.

  Mitochondria-associated endoplasmic reticulum membranes (MAMs) regulate ATG14- and Beclin1-mediated mitophagy and play key roles in the development of diabetic nephropathy (DN). DsbA-L is mainly located in MAMs and plays a role in renoprotection, but whether it activates mitophagy by maintaining MAM integrity remains unclear. In this study, we found that renal tubular damage was further aggravated in diabetic DsbA-L-/- mice compared to diabetic mice and that this damage was accompanied by disrupted MAM integrity and decreased mitophagy. Furthermore, notably decreased expression of ATG14 and Beclin1 in MAMs extracted from the kidneys of diabetic DsbA-L-/- mice was observed. In vitro, overexpression of DsbA-L reversed the disruption of MAM integrity and enhanced mitophagy in HK-2 cells, a human proximal tubular cell line, after exposure to high-glucose (HG) conditions. Additionally, compared to control mice, DsbA-L-/- mice were exhibited downregulated expression of helicase with zinc finger 2 (HELZ2) in their kidneys according to transcriptome analysis; HELZ2 serves as a cotranscription factor that synergistically functions with PPARα to promote the expression of mitofusin 2 (MFN-2). Treatment of HK-2 cells with MFN-2 siRNA resulted in MAM uncoupling and decreased mitophagy. Moreover, HG notably reduced the expression of HELZ2 and MFN-2 and inhibited mitophagy, and these effects were partially blocked by overexpression of DsbA-L and altered upon cotreatment with HELZ2 siRNA, HELZ2 overexpression or MK886 (PPARα inhibitor) treatment. These data indicate that DsbA-L alleviates diabetic tubular damage by activating mitophagy through maintenance of MAM integrity via the HELZ2/MFN-2 pathway.

Keywords:  DsbA-L; MAMs; Tubular injury; diabetic nephropathy; mitophagy

DOI:  https://doi.org/10.1042/CS20220787
Int J Mol Sci. 2023 May 20. pii: 9036. [Epub ahead of print]24(10):

Mitochondrial Connexins and Mitochondrial Contact Sites with Gap Junction Structure.

Selma Cetin-Ferra, Sharon C Francis, Anthonya T Cooper, Kit Neikirk, Andrea G Marshall, Antentor Hinton, Sandra A Murray.

  Mitochondria contain connexins, a family of proteins that is known to form gap junction channels. Connexins are synthesized in the endoplasmic reticulum and oligomerized in the Golgi to form hemichannels. Hemichannels from adjacent cells dock with one another to form gap junction channels that aggregate into plaques and allow cell-cell communication. Cell-cell communication was once thought to be the only function of connexins and their gap junction channels. In the mitochondria, however, connexins have been identified as monomers and assembled into hemichannels, thus questioning their role solely as cell-cell communication channels. Accordingly, mitochondrial connexins have been suggested to play critical roles in the regulation of mitochondrial functions, including potassium fluxes and respiration. However, while much is known about plasma membrane gap junction channel connexins, the presence and function of mitochondrial connexins remain poorly understood. In this review, the presence and role of mitochondrial connexins and mitochondrial/connexin-containing structure contact sites will be discussed. An understanding of the significance of mitochondrial connexins and their connexin contact sites is essential to our knowledge of connexins' functions in normal and pathological conditions, and this information may aid in the development of therapeutic interventions in diseases linked to mitochondria.

Keywords:  annular gap junctions; connexin; contact sites; mitochondria

DOI:  https://doi.org/10.3390/ijms24109036
J Dairy Sci. 2023 May 22. pii: S0022-0302(23)00275-8. [Epub ahead of print]

AMPK-endoplasmic reticulum stress axis contributes to lipopolysaccharide-caused mitochondrial dysfunction by regulating mitochondria-associated membrane function in bovine hepatocytes.

Wan Xie, Mengru Chen, Juan J Loor, Xiaokun Song, Nana Ma, Shendong Zhou, Hongzhu Zhang, Guangjun Chang, Xiangzhen Shen.

  Mitochondrial homeostasis is closely associated with cellular homeostasis process, whereas mitochondrial dysfunction contributes to apoptosis and mitophagy. Hence, analyzing the mechanism of lipopolysaccharide (LPS)-caused mitochondrial damage is necessary to understand how cellular homeostasis is maintained in bovine hepatocytes. Mitochondria-associated membranes (MAM), a connection between endoplasmic reticulum (ER) and mitochondria, is important to control mitochondrial function. To investigate the underlying mechanisms of the LPS-caused mitochondrial dysfunction, hepatocytes isolated from dairy cows at ∼160 d in milk (DIM) were pretreated with the specific inhibitors of adenosine 5'-monophosphate-activated protein kinase (AMPK), ER stress, RNA-activated protein kinase-like ER kinase (PERK), inositol-requiring enzyme 1α (IRE1α), c-Jun N-terminal kinase, and autophagy followed by a 12 μg/mL LPS treatment. The results showed that inhibiting ER stress with 4-phenylbutyric acid decreased the levels of autophagy and mitochondrial damage with AMPK inactivation in LPS-treated hepatocytes. The AMPK inhibitor compound C pretreatment alleviated LPS-induced ER stress, autophagy and mitochondrial dysfunction by regulating the expression of MAM-related genes, such as mitofusin 2 (MFN2), PERK, and IRE1α. Moreover, inhibiting PERK and IRE1α mitigated autophagy and mitochondrial dynamic disruption by regulating the MAM function. Additionally, blocking c-Jun N-terminal kinase, the downstream sensor of IRE1α, could reduce the levels of autophagy and apoptosis and restore the balance of mitochondrial fusion and fission by modulating the B cell leukemia 2 (BCL-2)/BCL-2 interacting protein 1 (BECLIN1) complex in the LPS-treated bovine hepatocytes. Furthermore, autophagy blockage with chloroquine could intervene in LPS-caused apoptosis to restore mitochondrial function. Collectively, these findings suggest that the AMPK-ER stress axis is involved in the LPS-caused mitochondrial dysfunction by mediating the MAM activity in bovine hepatocytes.

Keywords:  adenosine 5′-monophosphate-activated protein kinase; bovine hepatocytes; endoplasmic reticulum stress; mitochondria-associated membranes; mitochondrial dysfunction

DOI:  https://doi.org/10.3168/jds.2022-22879
Cell Calcium. 2023 May 12. pii: S0143-4160(23)00065-9. [Epub ahead of print]113 102753

Interplay between calcium and endoplasmic reticulum stress.

Jody Groenendyk, Marek Michalak.

  Cellular homeostasis is crucial for the healthy functioning of the organism. Disruption of cellular homeostasis activates endoplasmic reticulum (ER) stress coping responses including the unfolded protein response (UPR). There are three ER resident stress sensors responsible for UPR activation - IRE1α, PERK and ATF6. Ca2+ signaling plays an important role in stress responses including the UPR and the ER is the main Ca2+ storage organelle and a source of Ca2+ for cell signaling. The ER contains many proteins involved in Ca2+ import/export/ storage, Ca2+ movement between different cellular organelles and ER Ca2+ stores refilling. Here we focus on selected aspects of ER Ca2+ homeostasis and its role in activation of the ER stress coping responses.

Keywords:  Calcium homeostasis; Endoplasmic reticulum; Membrane contact sites; Sarcoplasmic reticulum; Unfolded protein response

DOI:  https://doi.org/10.1016/j.ceca.2023.102753
Mol Cell. 2023 May 12. pii: S1097-2765(23)00321-0. [Epub ahead of print]

Metamorphic proteins at the basis of human autophagy initiation and lipid transfer.

Anh Nguyen, Francesca Lugarini, Céline David, Pouya Hosnani, Çağla Alagöz, Annabelle Friedrich, David Schlütermann, Barbora Knotkova, Anoshi Patel, Iwan Parfentev, Henning Urlaub, Michael Meinecke, Björn Stork, Alex C Faesen.

  Autophagy is a conserved intracellular degradation pathway that generates de novo double-membrane autophagosomes to target a wide range of material for lysosomal degradation. In multicellular organisms, autophagy initiation requires the timely assembly of a contact site between the ER and the nascent autophagosome. Here, we report the in vitro reconstitution of a full-length seven-subunit human autophagy initiation supercomplex built on a core complex of ATG13-101 and ATG9. Assembly of this core complex requires the rare ability of ATG13 and ATG101 to switch between distinct folds. The slow spontaneous metamorphic conversion is rate limiting for the self-assembly of the supercomplex. The interaction of the core complex with ATG2-WIPI4 enhances tethering of membrane vesicles and accelerates lipid transfer of ATG2 by both ATG9 and ATG13-101. Our work uncovers the molecular basis of the contact site and its assembly mechanisms imposed by the metamorphosis of ATG13-101 to regulate autophagosome biogenesis in space and time.

Keywords:  autophagy; autophagy initiation; lipid transfer; membrane-contact site; metabolism; protein metamorphosis

DOI:  https://doi.org/10.1016/j.molcel.2023.04.026
Circ Res. 2023 May 26. 132(11): 1465-1467

Rebalancing Cardiac Structure and Function With Synthetic Mitochondria-Endoplasmic Reticulum Tethers.

Prasanna Katti, Brian Glancy.



Keywords:  Editorial; attention; biology; ischemia; reperfusion

DOI:  https://doi.org/10.1161/CIRCRESAHA.123.322911