bims-mecosi 2024-10-20 papers

bims-mecosi

Biomed News

on Membrane contact sites

Issue of 2024–10–20
six papers selected by
Verena Kohler, Umeå University

The evolving landscape of ER-LD contact sites.
Visualizing VDAC1 in live cells using a tetracysteine tag.
The dynamic regulatory network of phosphatidic acid metabolism: a spotlight on substrate cycling between phosphatidic acid and diacylglycerol.
Readdressing the Localization of Apolipoprotein E (APOE) in Mitochondria-Associated Endoplasmic Reticulum (ER) Membranes (MAMs): An Investigation of the Hepatic Protein-Protein Interactions of APOE with the Mitochondrial Proteins Lon Protease (LONP1), Mitochondrial Import Receptor Subunit TOM40 (TOMM40) and Voltage-Dependent Anion-Selective Channel 1 (VDAC1).
TRPV4 modulation affects mitochondrial parameters in adipocytes and its inhibition upregulates lipid accumulation.
Astrocytic lactoferrin deficiency augments MPTP-induced dopaminergic neuron loss by disturbing glutamate/calcium and ER-mitochondria signaling.

Front Cell Dev Biol. 2024 ;12 1483902

The evolving landscape of ER-LD contact sites.

Akhil Kumar, Surabhi Yadav, Vineet Choudhary.

  Lipid droplets (LDs) are evolutionarily conserved dynamic organelles that play an important role in cellular physiology. Growing evidence suggests that LD biogenesis occurs at discrete endoplasmic reticulum (ER) subdomains demarcated by the lipodystrophy protein, Seipin, lack of which impairs adipogenesis. However, the mechanisms of how these domains are selected is not completely known. These ER sites undergo ordered assembly of proteins and lipids to initiate LD biogenesis and facilitate establishment of ER-LD contact sites, a prerequisite for proper growth and maturation of droplets. LDs retain both physical and functional association with the ER throughout their lifecycle to facilitate bi-directional communication, such as exchange of proteins and lipids between the two organelles at these ER-LD contact sites. In recent years several molecular tethers have been identified that bridge ER and LDs together including few proteins that are found exclusively at these ER-LD contact interface. Here, we discuss recent advances in understanding the role of factors that ensure functionality of ER-LD contact site machinery for LD homeostasis.

Keywords:  ER-LD contact site; fatty acids; lipid droplets; lipid storage disorders; lipotoxicity; neutral lipid storage; organelle biogenesis; seipin

DOI:  https://doi.org/10.3389/fcell.2024.1483902
PLoS One. 2024 ;19(10): e0311107

Visualizing VDAC1 in live cells using a tetracysteine tag.

Johannes Pilic, Furkan E Oflaz, Benjamin Gottschalk, Yusuf C Erdogan, Wolfgang F Graier, Roland Malli.

The voltage-dependent anion channel 1 (VDAC1) is a crucial gatekeeper in the outer mitochondrial membrane, controlling metabolic and energy homeostasis. The available methodological approaches fell short of accurate visualization of VDAC1 in living cells. To permit precise VDAC1 imaging, we utilized the tetracysteine (TC)-tag and visualized VDAC1 dynamics in living cells. TC-tagged VDAC1 had a cluster-like distribution on mitochondria. The labeling of TC-tagged VDAC1 was validated with immunofluorescence. The majority of VDAC1-TC-clusters were localized at endoplasmic reticulum (ER)-mitochondria contact sites. Notably, VDAC1 colocalized with BCL-2 Antagonist/Killer (BAK)-clusters upon apoptotic stimulation. Using this new tool, we were able to observe VDAC1-TC at mitochondrial fission sites. These findings highlight the suitability of the TC-tag for live-cell imaging of VDAC1, shedding light on the roles of VDAC1 in cellular processes.

DOI: https://doi.org/10.1371/journal.pone.0311107
Biochem Soc Trans. 2024 Oct 17. pii: BST20231511. [Epub ahead of print]

The dynamic regulatory network of phosphatidic acid metabolism: a spotlight on substrate cycling between phosphatidic acid and diacylglycerol.

Reika Tei.

  Mammalian cells utilize over 1000 different lipid species to maintain cell and organelle membrane properties, control cell signaling and processes, and store energy. Lipid synthesis and metabolism are mediated by highly interconnected and spatiotemporally regulated networks of lipid-metabolizing enzymes and supported by vesicle trafficking and lipid-transfer at membrane contact sites. However, the regulatory mechanisms that achieve lipid homeostasis are largely unknown. Phosphatidic acid (PA) serves as the central hub for phospholipid biosynthesis, acting as a key intermediate in both the Kennedy pathway and the CDP-DAG pathway. Additionally, PA is a potent signaling molecule involved in various cellular processes. This dual role of PA, both as a critical intermediate in lipid biosynthesis and as a significant signaling molecule, suggests that it is tightly regulated within cells. This minireview will summarize the functional diversity of PA molecules based on their acyl tail structures and subcellular localization, highlighting recent tools and findings that shed light on how the physical, chemical, and spatial properties of PA species contribute to their differential metabolic fates and functions. Dysfunctional effects of altered PA metabolism as well as the strategies cells employ to maintain PA regulation and homeostasis will also be discussed. Furthermore, this review will explore the differential regulation of PA metabolism across distinct subcellular membranes. Our recent proximity labeling studies highlight the possibility that substrate cycling between PA and DAG may be location-dependent and have functional significance in cell signaling and lipid homeostasis.

Keywords:  cell homeostasis; lipid metabolism; lipid transfer; membranes; phosphatidic acids; phospholipases

DOI:  https://doi.org/10.1042/BST20231511
Int J Mol Sci. 2024 Oct 01. pii: 10597. [Epub ahead of print]25(19):

Readdressing the Localization of Apolipoprotein E (APOE) in Mitochondria-Associated Endoplasmic Reticulum (ER) Membranes (MAMs): An Investigation of the Hepatic Protein-Protein Interactions of APOE with the Mitochondrial Proteins Lon Protease (LONP1), Mitochondrial Import Receptor Subunit TOM40 (TOMM40) and Voltage-Dependent Anion-Selective Channel 1 (VDAC1).

Johanna Rueter, Gerald Rimbach, Stephanie Bilke, Andreas Tholey, Patricia Huebbe.

  As a component of circulating lipoproteins, APOE binds to cell surface receptors mediating lipoprotein metabolism and cholesterol transport. A growing body of evidence, including the identification of a broad variety of cellular proteins interacting with APOE, suggests additional independent functions. Investigating cellular localization and protein-protein interactions in cultured human hepatocytes, we aimed to contribute to the elucidation of hitherto unnoted cellular functions of APOE. We observed a strong accumulation of APOE in MAMs, equally evident for the two major isoforms APOE3 and APOE4. Using mass spectrometry proteome analyses, novel and previously noted APOE interactors were identified, including the mitochondrial proteins TOMM40, LONP1 and VDAC1. All three interactors were present in MAM fractions, which we think initially facilitates interactions with APOE. LONP1 is a protease with chaperone activity, which migrated to MAMs in response to ER stress, displaying a reinforced interaction with APOE. We therefore hypothesize that APOE may help in the unfolded protein response (UPR) by acting as a co-chaperone in cooperation with LONP1 at the interface of mitochondria and ER membranes. The interaction of APOE with the integral proteins TOMM40 and VDAC1 may point to the formation of bridging complexes connecting mitochondria with other organelles.

Keywords:  APOE4; chaperone; co-immunoprecipitation; liver; mitochondria–ER contacts; stress response; thapsigargin

DOI:  https://doi.org/10.3390/ijms251910597
Life Sci. 2024 Oct 14. pii: S0024-3205(24)00720-3. [Epub ahead of print] 123130

TRPV4 modulation affects mitochondrial parameters in adipocytes and its inhibition upregulates lipid accumulation.

Shamit Kumar, Tusar Kanta Acharya, Satish Kumar, Parnasree Mahapatra, Young-Tae Chang, Chandan Goswami.

  Enhanced lipid-droplet formation by adipocytes is a complex process and relevant for obesity. Using knock-out animals, involvement of TRPV4, a thermosensitive ion channel in the obesity has been proposed. However, exact role/s of TRPV4 in adipogenesis and obesity remain unclear and contradictory. Here we used in vitro culture of 3T3L-1 preadipocytes and primary murine-mesenchymal stem cells as model systems, and a series of live-cell-imaging to analyse the direct involvement of TRPV4 exclusively at the adipocytes that are free from other complex signalling as expected in in-vivo condition. Functional TRPV4 is endogenously expressed in pre- and in mature-adipocytes. Pharmacological inhibition of TRPV4 enhances differentiation of preadipocytes to mature adipocytes, increases expression of adipogenic and lipogenic genes, enhances cholesterol, promotes bigger lipid-droplet formation and reduces the lipid droplet temperature. On the other hand, TRPV4 activation enhanced the browning of adipocytes with increased UCP-1 levels. TRPV4 regulates mitochondrial-temperature, Ca2+-load, ATP, superoxides, cardiolipin, membrane potential (ΔΨm), and lipid-mitochondrial contact sites. TRPV4 also regulates the extent of actin fibres, affecting the cells mechanosensing ability. These findings link TRPV4-mediated mitochondrial changes in the context of lipid-droplet formation involved in adipogenesis and confirm the direct involvement of TRPV4 in adipogenesis. These findings may have broad implication in treating adipogenesis and obesity in future.

Keywords:  ATP; Adipogenesis; F-actin; Lipid droplet; ROS; TRPV4

DOI:  https://doi.org/10.1016/j.lfs.2024.123130
Free Radic Biol Med. 2024 Oct 13. pii: S0891-5849(24)00986-9. [Epub ahead of print]225 374-387

Astrocytic lactoferrin deficiency augments MPTP-induced dopaminergic neuron loss by disturbing glutamate/calcium and ER-mitochondria signaling.

Shuang-Feng Xu, Jun-He Cui, Xin Liu, Zhong-Qiu Pang, Chen-Yang Bai, Chao Jiang, Chuang Luan, Yun-Peng Li, Yan Zhao, Yi-Ming You, Chuang Guo.

  Increased levels of lactoferrin (Lf) are present in the aged brain and in the lesions of various neurodegenerative diseases, including Parkinson's disease (PD), and may contribute to the cascade of events involved in neurodevelopment and neuroprotection. However, whether Lf originates from astrocytes and functions within either the normal or pathological brain are unknown. Here, we employed mice with specific knockout of the astrocyte lactoferrin gene (named Lf-cKO) to explore its specific roles in the pathological process of PD. We observed a decrease in tyrosine hydroxylase-positive cells, mitochondrial dysfunction of residual dopaminergic neurons, and motor deficits in Lf-cKO mice, which were significantly aggravated after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. To further explore how astrocytic lactoferrin deficiency exacerbated PD-like manifestation in MPTP-treated mice, the critical molecules involved in endoplasmic reticulum (ER)-mitochondria contacts and signaling pathways were investigated. In vitro and in vivo models, we found an aberrant level of effects implicated in glutamate and calcium homeostasis, mitochondrial morphology and functions, mitochondrial dynamics, and mitochondria-associated ER membranes, accompanied by signs of oxidative stress and ER stress, which increase the fragility of dopaminergic neurons. These findings confirm the existence of astrocytic Lf and its influence on the fate of dopaminergic neurons by regulating glutamate/calcium metabolism and ER-mitochondria signaling. Our findings may be a promising target for the treatment of PD.

Keywords:  Astrocyte; Calcium homeostasis; Glutamate metabolism; Lactoferrin; Mitochondrial dysfunctions; Parkinson's disease

DOI:  https://doi.org/10.1016/j.freeradbiomed.2024.10.284