bims-mecosi 2024-01-14 papers

bims-mecosi

Biomed News

on Membrane contact sites

Issue of 2024–01–14
nine papers selected by
Verena Kohler, Umeå University

OSBP is a major determinant of Golgi phosphatidylinositol 4-phosphate homeostasis.
Stay in touch with the endoplasmic reticulum.
Mitochondrial phospholipid transport: Role of contact sites and lipid transport proteins.
A new GUV-based assay to reconstitute membrane tethering in vitro demonstrates the vesicle tethering ability of the selective autophagy scaffold Atg11.
CGI1746 targets σ1R to modulate ferroptosis through mitochondria-associated membranes.
The Protective Role of Mitochondria-Associated Endoplasmic Reticulum Membrane (MAM) Protein Sigma-1 Receptor in Regulating Endothelial Inflammation and Permeability Associated with Acute Lung Injury.
Super-Resolution Analysis of the Origins of the Elementary Events of ER Calcium Release in Dorsal Root Ganglion Neurons.
Distinct cellular expression and subcellular localization of Kv2 voltage-gated K+ channel subtypes in dorsal root ganglion neurons conserved between mice and humans.
Benzomorphan and non-benzomorphan agonists differentially alter sigma-1 receptor quaternary structure, as does types of cellular stress.

bioRxiv. 2023 Dec 22. pii: 2023.12.21.572879. [Epub ahead of print]

OSBP is a major determinant of Golgi phosphatidylinositol 4-phosphate homeostasis.

Colleen P Doyle, Liz Timple, Gerald R V Hammond.

  The lipid phosphatidylinositol 4-phosphate (PI4P) plays a master regulatory role at Golgi membranes, orchestrating membrane budding, non-vesicular lipid transport and membrane organization. It follows that harmonious Golgi function requires strictly maintained PI4P homeostasis. One of the most abundant PI4P effector proteins is the oxysterol binding protein (OSBP), a lipid transfer protein that exchanges trans Golgi PI4P for ER cholesterol. Although this protein consumes PI4P as part of its lipid anti-porter function, whether it actively contributes to Golgi PI4P homeostasis has been questioned. Here, we employed a series of acute and chronic genetic manipulations, together with orthogonal targeting of OSBP, to interrogate its control over Golgi PI4P abundance. Modulating OSBP levels at ER:Golgi membrane contact sites produces reciprocal changes in PI4P levels. Additionally, we observe that OSBP has a high capacity for PI4P turnover, even at orthogonal organelle membranes. However, despite also visiting the plasma membrane, endogenous OSBP makes no impact on PI4P levels in this compartment. We conclude that OSBP is a major determinant of Golgi PI4P homeostasis.

Keywords:  Lipid transfer proteins; PtdIns4P; membrane contact sites; phosphoinositides

DOI:  https://doi.org/10.1101/2023.12.21.572879
Sci China Life Sci. 2024 Jan 04.

Stay in touch with the endoplasmic reticulum.

Sha Sun, Gan Zhao, Mingkang Jia, Qing Jiang, Shulin Li, Haibin Wang, Wenjing Li, Yunyun Wang, Xin Bian, Yan G Zhao, Xun Huang, Ge Yang, Huaqing Cai, Jose C Pastor-Pareja, Liang Ge, Chuanmao Zhang, Junjie Hu.

  The endoplasmic reticulum (ER), which is composed of a continuous network of tubules and sheets, forms the most widely distributed membrane system in eukaryotic cells. As a result, it engages a variety of organelles by establishing membrane contact sites (MCSs). These contacts regulate organelle positioning and remodeling, including fusion and fission, facilitate precise lipid exchange, and couple vital signaling events. Here, we systematically review recent advances and converging themes on ER-involved organellar contact. The molecular basis, cellular influence, and potential physiological functions for ER/nuclear envelope contacts with mitochondria, Golgi, endosomes, lysosomes, lipid droplets, autophagosomes, and plasma membrane are summarized.

Keywords:  Golgi apparatus; autophagosome; endoplasmic reticulum; endosome; lipid droplets; lysosome; membrane contact site; mitochondria; nuclear envelope; plasma membrane

DOI:  https://doi.org/10.1007/s11427-023-2443-9
Prog Lipid Res. 2024 Jan 07. pii: S0163-7827(24)00001-8. [Epub ahead of print]94 101268

Mitochondrial phospholipid transport: Role of contact sites and lipid transport proteins.

Vijay Aditya Mavuduru, Lavanya Vadupu, Krishna Kanta Ghosh, Sabyasachi Chakrabortty, Balázs Gulyás, Parasuraman Padmanabhan, Writoban Basu Ball.

  One of the major constituents of mitochondrial membranes is the phospholipids, which play a key role in maintaining the structure and the functions of the mitochondria. However, mitochondria do not synthesize most of the phospholipids in situ, necessitating the presence of phospholipid import pathways. Even for the phospholipids, which are synthesized within the inner mitochondrial membrane (IMM), the phospholipid precursors must be imported from outside the mitochondria. Therefore, the mitochondria heavily rely on the phospholipid transport pathways for its proper functioning. Since, mitochondria are not part of a vesicular trafficking network, the molecular mechanisms of how mitochondria receive its phospholipids remain a relevant question. One of the major ways that hydrophobic phospholipids can cross the aqueous barrier of inter or intraorganellar spaces is by apposing membranes, thereby decreasing the distance of transport, or by being sequestered by lipid transport proteins (LTPs). Therefore, with the discovery of LTPs and membrane contact sites (MCSs), we are beginning to understand the molecular mechanisms of phospholipid transport pathways in the mitochondria. In this review, we will present a brief overview of the recent findings on the molecular architecture and the importance of the MCSs, both the intraorganellar and interorganellar contact sites, in facilitating the mitochondrial phospholipid transport. In addition, we will also discuss the role of LTPs for trafficking phospholipids through the intermembrane space (IMS) of the mitochondria. Mechanistic insights into different phospholipid transport pathways of mitochondria could be exploited to vary the composition of membrane phospholipids and gain a better understanding of their precise role in membrane homeostasis and mitochondrial bioenergetics.

Keywords:  ERMES; Mitochondria; Mitochondrial contact sites; Phospholipid biosynthesis; Phospholipid transport; vCLAMP

DOI:  https://doi.org/10.1016/j.plipres.2024.101268
bioRxiv. 2023 Dec 19. pii: 2023.12.19.572332. [Epub ahead of print]

A new GUV-based assay to reconstitute membrane tethering in vitro demonstrates the vesicle tethering ability of the selective autophagy scaffold Atg11.

Devika Andhare, Michael J Ragusa.

Membrane tethering is essential for the generation of organelle contact sites and to anchor incoming vesicles to their target membranes before vesicle fusion. During autophagy in yeast, tethering of 30 nm vesicles to cargo is one of the first steps in the generation of the isolation membrane that engulfs the cargo to be degraded. While membrane tethering is critical for cellular function, many of the current biochemical techniques to assay for membrane tethering rely on indirect readouts and are limited in their ability to monitor protein localization at sites of tethering. As such, we developed a fluorescence-microscopy-based G UV liposome tethering assay (GLT) to directly visualize membrane tethering and monitor protein localization at tethering sites simultaneously. We initially used GLT with engineered membrane tethers to demonstrate the ease of use, versatility and sensitivity of the assay. We also demonstrated that the selective autophagy scaffolding protein Atg11 can bind, and tether negatively charged membranes but is unable to bind GUVs mimicking the charge of the outer mitochondrial membrane. Atg11 instead requires the selective autophagy receptor Atg32 to be recruited to mitochondrial membranes. Lastly, we demonstrate that Atg11 bound to Atg32 on GUVs can tether negatively charged vesicles to GUVs. Collectively, our results reconstitute one of the first steps during the initiation of mitochondrial autophagy and highlight the versatility of GLT to study a range of membrane tethering events biochemically.

DOI: https://doi.org/10.1101/2023.12.19.572332
Nat Chem Biol. 2024 Jan 11.

CGI1746 targets σ1R to modulate ferroptosis through mitochondria-associated membranes.

Zili Zhang, Hong Zhou, Wenjia Gu, Yuehan Wei, Shan Mou, Youjun Wang, Jing Zhang, Qing Zhong.

Ferroptosis is iron-dependent oxidative cell death. Labile iron and polyunsaturated fatty acid (PUFA)-containing lipids are two critical factors for ferroptosis execution. Many processes regulating iron homeostasis and lipid synthesis are critically involved in ferroptosis. However, it remains unclear whether biological processes other than iron homeostasis and lipid synthesis are associated with ferroptosis. Using kinase inhibitor library screening, we discovered a small molecule named CGI1746 that potently blocks ferroptosis. Further studies demonstrate that CGI1746 acts through sigma-1 receptor (σ1R), a chaperone primarily located at mitochondria-associated membranes (MAMs), to inhibit ferroptosis. Suppression of σ1R protects mice from cisplatin-induced acute kidney injury hallmarked by ferroptosis. Mechanistically, CGI1746 treatment or genetic disruption of MAMs leads to defective Ca2+ transfer, mitochondrial reactive oxygen species (ROS) production and PUFA-containing triacylglycerol accumulation. Therefore, we propose a critical role for MAMs in ferroptosis execution.

DOI: https://doi.org/10.1038/s41589-023-01512-1
Cells. 2023 Dec 19. pii: 5. [Epub ahead of print]13(1):

The Protective Role of Mitochondria-Associated Endoplasmic Reticulum Membrane (MAM) Protein Sigma-1 Receptor in Regulating Endothelial Inflammation and Permeability Associated with Acute Lung Injury.

Zahra Mahamed, Mohammad Shadab, Rauf Ahmad Najar, Michelle Warren Millar, Jashandeep Bal, Traci Pressley, Fabeha Fazal.

  Earlier studies from our lab identified endoplasmic reticulum (ER) chaperone BiP/GRP78, an important component of MAM, to be a novel determinant of endothelial cell (EC) dysfunction associated with acute lung injury (ALI). Sigma1R (Sig1R) is another unique ER receptor chaperone that has been identified to associate with BiP/GRP78 at the MAM and is known to be a pluripotent modulator of cellular homeostasis. However, it is unclear if Sig1R also plays a role in regulating the EC inflammation and permeability associated with ALI. Our data using human pulmonary artery endothelial cells (HPAECs) showed that siRNA-mediated knockdown of Sig1R potentiated LPS-induced the expression of proinflammatory molecules ICAM-1, VCAM-1 and IL-8. Consistent with this, Sig1R agonist, PRE-084, known to activate Sig1R by inducing its dissociation from BiP/GRP78, blunted the above response. Notably, PRE-084 failed to blunt LPS-induced inflammatory responses in Sig1R-depleted cells, confirming that the effect of PRE-084 is driven by Sig1R. Furthermore, Sig1R antagonist, NE-100, known to inactivate Sig1R by blocking its dissociation from BiP/GRP78, failed to block LPS-induced inflammatory responses, establishing that dissociation from BiP/GRP78 is required for Sig1R to exert its anti-inflammatory action. Unlike Sig1R, the siRNA-mediated knockdown or Subtilase AB-mediated inactivation of BiP/GRP78 protected against LPS-induced EC inflammation. Interestingly, the protective effect of BiP/GRP78 knockdown or inactivation was abolished in cells that were depleted of Sig1R, confirming that BiP/GRP78 knockdown/inactivation-mediated suppression of EC inflammation is mediated via Sig1R. In view of these findings, we determined the in vivo relevance of Sig1R in a mouse model of sepsis-induced ALI. The intraperitoneal injection of PRE-084 mitigated sepsis-induced ALI, as evidenced by a decrease in ICAM-1, IL-6 levels, lung PMN infiltration, and lung vascular leakage. Together, these data evidence a protective role of Sig1R against endothelial dysfunction associated with ALI and identify it as a viable target in terms of controlling ALI in sepsis.

Keywords:  acute lung injury; endothelial cells; immunoglobulin-binding protein; inflammation; mitochondria-associated endoplasmic reticulum membranes; permeability; sigma 1 receptor

DOI:  https://doi.org/10.3390/cells13010005
Cells. 2023 Dec 23. pii: 38. [Epub ahead of print]13(1):

Super-Resolution Analysis of the Origins of the Elementary Events of ER Calcium Release in Dorsal Root Ganglion Neurons.

Miriam E Hurley, Shihab S Shah, Thomas M D Sheard, Hannah M Kirton, Derek S Steele, Nikita Gamper, Izzy Jayasinghe.

  Coordinated events of calcium (Ca2+) released from the endoplasmic reticulum (ER) are key second messengers in excitable cells. In pain-sensing dorsal root ganglion (DRG) neurons, these events can be observed as Ca2+ sparks, produced by a combination of ryanodine receptors (RyR) and inositol 1,4,5-triphosphate receptors (IP3R1). These microscopic signals offer the neuronal cells with a possible means of modulating the subplasmalemmal Ca2+ handling, initiating vesicular exocytosis. With super-resolution dSTORM and expansion microscopies, we visualised the nanoscale distributions of both RyR and IP3R1 that featured loosely organised clusters in the subplasmalemmal regions of cultured rat DRG somata. We adapted a novel correlative microscopy protocol to examine the nanoscale patterns of RyR and IP3R1 in the locality of each Ca2+ spark. We found that most subplasmalemmal sparks correlated with relatively small groups of RyR whilst larger sparks were often associated with larger groups of IP3R1. These data also showed spontaneous Ca2+ sparks in <30% of the subplasmalemmal cell area but consisted of both these channel species at a 3.8-5 times higher density than in nonactive regions of the cell. Taken together, these observations reveal distinct patterns and length scales of RyR and IP3R1 co-clustering at contact sites between the ER and the surface plasmalemma that encode the positions and the quantity of Ca2+ released at each Ca2+ spark.

Keywords:  calcium signalling; correlative microscopy; dSTORM; dorsal root ganglion neurons; expansion microscopy; inositol 1,4,5-trisphosphate receptor; ryanodine receptor

DOI:  https://doi.org/10.3390/cells13010038
bioRxiv. 2023 Dec 24. pii: 2023.03.01.530679. [Epub ahead of print]

Distinct cellular expression and subcellular localization of Kv2 voltage-gated K+ channel subtypes in dorsal root ganglion neurons conserved between mice and humans.

Robert G Stewart, Miriam Camacena, Bryan A Copits, Jon T Sack.

  The distinct organization of Kv2 voltage-gated potassium channels on and near the cell body of brain neurons enables their regulation of action potentials and specialized membrane contact sites. Somatosensory neurons have a pseudounipolar morphology and transmit action potentials from peripheral nerve endings through axons that bifurcate to the spinal cord and the cell body within ganglia including the dorsal root ganglia (DRG). Kv2 channels regulate action potentials in somatosensory neurons, yet little is known about where Kv2 channels are located. Here we define the cellular and subcellular localization of the Kv2 paralogs, Kv2.1 and Kv2.2, in DRG somatosensory neurons with a panel of antibodies, cell markers, and genetically modified mice. We find that relative to spinal cord neurons, DRG neurons have similar levels of detectable Kv2.1, and higher levels of Kv2.2. In older mice, detectable Kv2.2 remains similar while detectable Kv2.1 decreases. Both Kv2 subtypes adopt clustered subcellular patterns that are distinct from central neurons. Most DRG neurons co-express Kv2.1 and Kv2.2, although neuron subpopulations show preferential expression of Kv2.1 or Kv2.2. We find that Kv2 protein expression and subcellular localization is similar between mouse and human DRG neurons. We conclude that the organization of both Kv2 channels is consistent with physiological roles in the somata and stem axons of DRG neurons. The general prevalence of Kv2.2 in DRG as compared to central neurons and the enrichment of Kv2.2 relative to detectable Kv2.1, in older mice, proprioceptors, and axons suggest more widespread roles for Kv2.2 in DRG neurons.

Keywords:  Dorsal root ganglion; Kv2.1; Kv2.2; Somatosensory neurons; Voltage gated ion channels

DOI:  https://doi.org/10.1101/2023.03.01.530679
Cell Mol Life Sci. 2024 Jan 09. 81(1): 14

Benzomorphan and non-benzomorphan agonists differentially alter sigma-1 receptor quaternary structure, as does types of cellular stress.

Simon Couly, Yuko Yasui, Semnyonga Foncham, Ioannis Grammatikakis, Ashish Lal, Lei Shi, Tsung-Ping Su.

  Sigma-1 receptor (S1R) is a calcium-sensitive, ligand-operated receptor chaperone present on the endoplasmic reticulum (ER) membrane. S1R plays an important role in ER-mitochondrial inter-organelle calcium signaling and cell survival. S1R and its agonists confer resilience against various neurodegenerative diseases; however, the molecular mechanism of S1R is not yet fully understood. At resting state, S1R is either in a monomeric or oligomeric state but the ratio of these concentrations seems to change upon activation of S1R. S1R is activated by either cellular stress, such as ER-calcium depletion, or ligands. While the effect of ligands on S1R quaternary structure remains unclear, the effect of cellular stress has not been studied. In this study we utilize cellular and an in-vivo model to study changes in quaternary structure of S1R upon activation. We incubated cells with cellular stressors (H2O2 and thapsigargin) or exogenous ligands, then quantified monomeric and oligomeric forms. We observed that benzomorphan-based S1R agonists induce monomerization of S1R and decrease oligomerization, which was confirmed in the liver tissue of mice injected with (+)-Pentazocine. Antagonists block this effect but do not induce any changes when used alone. Oxidative stress (H2O2) increases the monomeric/oligomeric S1R ratio whereas ER calcium depletion (thapsigargin) has no effect. We also analyzed the oligomerization ability of various truncated S1R fragments and identified the fragments favorizing oligomerization. In this publication we demonstrate that quaternary structural changes differ according to the mechanism of S1R activation. Therefore, we offer a novel perspective on S1R activation as a nuanced phenomenon dependent on the type of stimulus.

Keywords:  Endoplasmic reticulum; MAM; Mitochondria; Neurodegenerative disorders; Sigma-1 receptor

DOI:  https://doi.org/10.1007/s00018-023-05023-z