bims-mecosi Biomed News
on Membrane contact sites
Issue of 2024‒02‒11
nine papers selected by
Verena Kohler, Umeå University
  1. Remodelling of mitochondrial function by import of specific lipids at multiple membrane-contact sites.
  2. Orthogonal Targeting of SAC1 to Mitochondria Implicates ORP2 as a Major Player in PM PI4P Turnover.
  3. Contact-FP: A Dimerization-Dependent Fluorescent Protein Toolkit for Visualizing Membrane Contact Site Dynamics.
  4. Mitochondria-Endoplasmic Reticulum Contact Sites (MERCS): A New Axis in Neuronal Degeneration and Regeneration.
  5. Mapping the lipidome in mitochondria-associated membranes (MAMs) in an in vitro model of Alzheimer's disease.
  6. A role for Vps13-mediated lipid transfer at the ER-endosome contact site in ESCRT-mediated sorting.
  7. VDR regulates mitochondrial function as a protective mechanism against renal tubular cell injury in diabetic rats.
  8. Mfn2/Hsc70 Complex Mediates the Formation of Mitochondria-Lipid Droplets Membrane Contact and Regulates Myocardial Lipid Metabolism.
  9. Distinct cellular expression and subcellular localization of Kv2 voltage-gated K+ channel subtypes in dorsal root ganglion neurons conserved between mice and humans.
  1. FEBS Lett. 2024 Feb 04.
    Remodelling of mitochondrial function by import of specific lipids at multiple membrane-contact sites.
    Aksel J Saukko-Paavola, Robin W Klemm.
      Organelles form physical and functional contact between each other to exchange information, metabolic intermediates, and signaling molecules. Tethering factors and contact site complexes bring partnering organelles into close spatial proximity to establish membrane contact sites (MCSs), which specialize in unique functions like lipid transport or Ca2+ signaling. Here, we discuss how MCSs form dynamic platforms that are important for lipid metabolism. We provide a perspective on how import of specific lipids from the ER and other organelles may contribute to remodeling of mitochondria during nutrient starvation. We speculate that mitochondrial adaptation is achieved by connecting several compartments into a highly dynamic organelle network. The lipid droplet appears to be a central hub in coordinating the function of these organelle neighborhoods.
    Keywords:  autophagy; endoplasmic reticulum (ER); lipid droplets (LDs); membrane contact sites; metabolic adaptation; mitochondria; mitochondrial shape; organelle-network; starvation
    DOI:  https://doi.org/10.1002/1873-3468.14813
  2. Contact (Thousand Oaks). 2024 Jan-Dec;7:7 25152564241229272
    Orthogonal Targeting of SAC1 to Mitochondria Implicates ORP2 as a Major Player in PM PI4P Turnover.
    Colleen P Doyle, Andrew Rectenwald, Liz Timple, Gerald R V Hammond.
      Oxysterol-binding protein (OSBP)-related proteins (ORPs) 5 and 8 have been shown to deplete the lipid phosphatidylinositol 4-phosphate (PI4P) at sites of membrane contact between the endoplasmic reticulum (ER) and plasma membrane (PM). This is believed to be caused by transport of PI4P from the PM to the ER, where PI4P is degraded by an ER-localized SAC1 phosphatase. This is proposed to power the anti-port of phosphatidylserine (PS) lipids from ER to PM, up their concentration gradient. Alternatively, ORPs have been proposed to sequester PI4P, dependent on the concentration of their alternative lipid ligand. Here, we aimed to distinguish these possibilities in living cells by orthogonal targeting of PI4P transfer and degradation to PM-mitochondria contact sites. Surprisingly, we found that orthogonal targeting of SAC1 to mitochondria enhanced PM PI4P turnover independent of targeting to contact sites with the PM. This turnover could be slowed by knock-down of soluble ORP2, which also has a major impact on PM PI4P levels even without SAC1 over-expression. The data reveal a role for contact site-independent modulation of PM PI4P levels and lipid antiport.
    Keywords:  PtdIns4P; lipid transfer proteins; membrane contact sites; phosphoinositides
    DOI:  https://doi.org/10.1177/25152564241229272
  3. Contact (Thousand Oaks). 2024 Jan-Dec;7:7 25152564241228911
    Contact-FP: A Dimerization-Dependent Fluorescent Protein Toolkit for Visualizing Membrane Contact Site Dynamics.
    Gregory E Miner, Sidney Y Smith, Wendy K Showalter, Christina M So, Joey V Ragusa, Alex E Powers, Maria Clara Zanellati, Chih-Hsuan Hsu, Michelle F Marchan, Sarah Cohen.
      Membrane contact sites (MCSs) are sites of close apposition between two organelles used to exchange ions, lipids, and information. Cells respond to changing environmental or developmental conditions by modulating the number, extent, or duration of MCSs. Because of their small size and dynamic nature, tools to study the dynamics of MCSs in live cells have been limited. Dimerization-dependent fluorescent proteins (ddFPs) targeted to organelle membranes are an ideal tool for studying MCS dynamics because they reversibly interact to fluoresce specifically at the interface between two organelles. Here, we build on previous work using ddFPs as sensors to visualize the morphology and dynamics of MCSs. We engineered a suite of ddFPs called Contact-FP that targets ddFP monomers to lipid droplets (LDs), the endoplasmic reticulum (ER), mitochondria, peroxisomes, lysosomes, plasma membrane, caveolae, and the cytoplasm. We show that these probes correctly localize to their target organelles. Using LDs as a test case, we demonstrate that Contact-FP pairs specifically localize to the interface between two target organelles. Titration of LD-mitochondria ddFPs revealed that these sensors can be used at high concentrations to drive MCSs or can be titrated down to minimally perturb and visualize endogenous MCSs. We show that Contact-FP probes can be used to: (1) visualize LD-mitochondria MCS dynamics, (2) observe changes in LD-mitochondria MCS dynamics upon overexpression of PLIN5, a known LD-mitochondrial tether, and (3) visualize two MCSs that share one organelle simultaneously (e.g., LD-mitochondria and LD-ER MCSs). Contact-FP probes can be optimized to visualize MCSs between any pair of organelles represented in the toolkit.
    Keywords:  biosensors; caveolae; endoplasmic reticulum; fluorescent proteins; lipid droplets; lysosomes; membrane contact sites; mitochondria; organelles; peroxisomes; plasma membrane
    DOI:  https://doi.org/10.1177/25152564241228911
  4. Mol Neurobiol. 2024 Feb 06.
    Mitochondria-Endoplasmic Reticulum Contact Sites (MERCS): A New Axis in Neuronal Degeneration and Regeneration.
    Vijaya Harini Sathyamurthy, Yoghalakshmi Nagarajan, Venkatachalam Deepa Parvathi.
      Mitochondria-Endoplasmic Reticulum Contact Sites (MERCS) are dynamic structures whose physiological interaction is vital to direct life and death of the cell. A bevy of tethering proteins, mitofusin-1/2 (Mfn-1/2), glucose-regulated protein-75 (Grp-75), voltage-dependent anion channel-1 (VDAC1), and dynamic-related protein-1 (Drp1), plays an integral role in establishing and regulating this intricate intracellular communication. Dysregulation of this interplay leads to various neurodegenerative disorders, like Alzheimer's disease (AD), Parkinson's disease (PD), stroke, traumatic brain injury (TBI), amyotrophic lateral sclerosis (ALS), and frontotemporal dementia (FTD). Although there is an absence of a well-defined molecular background that dictates the pathway of MERCS, adequate exploration has resulted in preliminary data that suggests its cardinal role in neuroregeneration. The juxtaposition of mitochondria and ER has a critical function in cell senescence, thus regulating regeneration. Axonal regeneration and brain tissue regeneration, using reactive astrocytes, are studied most extensively. Overexpression of Grp-75 promoted axonal regeneration post a nerve injury. Attempts have been made to exploit MERCS as potential therapeutic drug targets for enhancing neuroregeneration and impeding neurodegeneration. Novel strategies have been developed to aid the delivery of mitochondria into the neuronal cell body, which in turn establishes a network with the presiding ER resulting in contact site formation. The fascinating aspect of this mechanism is that despite the lack of inherent regenerative capacity in neurons, it can be induced by modifying MERCS.
    Keywords:  Axonal regeneration; Mitochondria-Endoplasmic Reticulum Contact Sites (MERCS); Neurodegenerative diseases; Targeted therapy
    DOI:  https://doi.org/10.1007/s12035-024-03971-6
  5. J Neurochem. 2024 Feb 07.
    Mapping the lipidome in mitochondria-associated membranes (MAMs) in an in vitro model of Alzheimer's disease.
    Tânia Fernandes, Tânia Melo, Tiago Conde, Bruna Neves, Pedro Domingues, Rosa Resende, Cláudia F Pereira, Paula I Moreira, Maria Rosário Domingues.
      The disruption of mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) plays a relevant role in Alzheimer's disease (AD). MAMs have been implicated in neuronal dysfunction and death since it is associated with impairment of functions regulated in this subcellular domain, including lipid synthesis and trafficking, mitochondria dysfunction, ER stress-induced unfolded protein response (UPR), apoptosis, and inflammation. Since MAMs play an important role in lipid metabolism, in this study we characterized and investigated the lipidome alterations at MAMs in comparison with other subcellular fractions, namely microsomes and mitochondria, using an in vitro model of AD, namely the mouse neuroblastoma cell line (N2A) over-expressing the APP familial Swedish mutation (APPswe) and the respective control (WT) cells. Phospholipids (PLs) and fatty acids (FAs) were isolated from the different subcellular fractions and analyzed by HILIC-LC-MS/MS and GC-MS, respectively. In this in vitro AD model, we observed a down-regulation in relative abundance of some phosphatidylcholine (PC), lysophosphatidylcholine (LPC), and lysophosphatidylethanolamine (LPE) species with PUFA and few PC with saturated and long-chain FA. We also found an up-regulation of CL, and antioxidant alkyl acyl PL. Moreover, multivariate analysis indicated that each organelle has a specific lipid profile adaptation in N2A APPswe cells. In the FAs profile, we found an up-regulation of C16:0 in all subcellular fractions, a decrease of C18:0 levels in total fraction (TF) and microsomes fraction, and a down-regulation of 9-C18:1 was also found in mitochondria fraction in the AD model. Together, these results suggest that the over-expression of the familial APP Swedish mutation affects lipid homeostasis in MAMs and other subcellular fractions and supports the important role of lipids in AD physiopathology.
    Keywords:  Alzheimer's disease; ER-mitochondria contacts; lipid dyshomeostasis; lipidomics; subcellular fractions
    DOI:  https://doi.org/10.1111/jnc.16072
  6. J Cell Biol. 2024 Apr 01. pii: e202307094. [Epub ahead of print]223(4):
    A role for Vps13-mediated lipid transfer at the ER-endosome contact site in ESCRT-mediated sorting.
    Sho W Suzuki, Matthew West, Yichen Zhang, Jenny S Fan, Rachel T Roberts, Greg Odorizzi, Scott D Emr.
      Endosomes are specialized organelles that function in the secretory and endocytic protein sorting pathways. Endocytosed cell surface receptors and transporters destined for lysosomal degradation are sorted into intraluminal vesicles (ILVs) at endosomes by endosomal sorting complexes required for transport (ESCRT) proteins. The endosomes (multivesicular bodies, MVBs) then fuse with the lysosome. During endosomal maturation, the number of ILVs increases, but the size of endosomes does not decrease despite the consumption of the limiting membrane during ILV formation. Vesicle-mediated trafficking is thought to provide lipids to support MVB biogenesis. However, we have uncovered an unexpected contribution of a large bridge-like lipid transfer protein, Vps13, in this process. Here, we reveal that Vps13-mediated lipid transfer at ER-endosome contact sites is required for the ESCRT pathway. We propose that Vps13 may play a critical role in supplying lipids to the endosome, ensuring continuous ESCRT-mediated sorting during MVB biogenesis.
    DOI:  https://doi.org/10.1083/jcb.202307094
  7. Redox Biol. 2024 Jan 26. pii: S2213-2317(24)00038-7. [Epub ahead of print]70 103062
    VDR regulates mitochondrial function as a protective mechanism against renal tubular cell injury in diabetic rats.
    Hong Chen, Hao Zhang, Ai-Mei Li, Yu-Ting Liu, Yan Liu, Wei Zhang, Cheng Yang, Na Song, Ming Zhan, Shikun Yang.
      PURPOSE: To investigate the regulatory effect and mechanism of Vitamin D receptor (VDR) on mitochondrial function in renal tubular epithelial cell under diabetic status.METHODS: The diabetic rats induced by streptozotocin (STZ) and HK-2 cells under high glocose(HG)/transforming growth factor beta (TGF-β) stimulation were used in this study. Calcitriol was administered for 24 weeks. Renal tubulointerstitial injury and some parameters of mitochondrial function including mitophagy, mitochondrial fission, mitochondrial ROS, mitochondrial membrane potential (MMP), mitochondrial ATP, Complex V activity and mitochondria-associated ER membranes (MAMs) integrity were examined. Additionally, paricalcitol, 3-MA (an autophagy inhibitor), VDR over-expression plasmid, VDR siRNA and Mfn2 siRNA were applied in vitro.
    RESULTS: The expression of VDR, Pink1, Parkin, Fundc1, LC3II, Atg5, Mfn2, Mfn1 in renal tubular cell of diabetic rats were decreased significantly. Calcitriol treatment reduced the levels of urinary albumin, serum creatinine and attenuated renal tubulointerstitial fibrosis in STZ induced diabetic rats. In addition, VDR agonist relieved mitophagy dysfunction, MAMs integrity, and inhibited mitochondrial fission, mitochondrial ROS. Co-immunoprecipitation analysis demonstrated that VDR interacted directly with Mfn2. Mitochondrial function including mitophagy, mitochondrial membrane potential (MMP), mitochondrial Ca2+, mitochondrial ATP and Complex V activity were decreased dramatically in HK-2 cells under HG/TGF-β ambience. In vitro pretreatment of HK-2 cells with autophagy inhibitor 3-MA, VDR siRNA or Mfn2 siRNA negated the activating effects of paricalcitol on mitochondrial function. Pricalcitol and VDR over-expression plasmid activated Mfn2 and then partially restored the MAMs integrity. Additionally, VDR restored mitophagy was partially associated with MAMs integrity through Fundc1.
    CONCLUSION: Activated VDR could contribute to restore mitophagy through Mfn2-MAMs-Fundc1 pathway in renal tubular cell. VDR could recover mitochondrial ATP, complex V activity and MAMs integrity, inhibit mitochondrial fission and mitochondrial ROS. It indicating that VDR agonists ameliorate renal tubulointerstitial fibrosis in diabetic rats partially via regulation of mitochondrial function.
    Keywords:  DN; MAMs; Mitochondrial; Renal tubular cell; VDR
    DOI:  https://doi.org/10.1016/j.redox.2024.103062
  8. Adv Sci (Weinh). 2024 Feb 04. e2307749
    Mfn2/Hsc70 Complex Mediates the Formation of Mitochondria-Lipid Droplets Membrane Contact and Regulates Myocardial Lipid Metabolism.
    Lang Hu, Daishi Tang, Bingchao Qi, Dong Guo, Ying Wang, Jing Geng, Xiaoliang Zhang, Liqiang Song, Pan Chang, Wensheng Chen, Feng Fu, Yan Li.
      The heart primarily derives its energy through lipid oxidation. In cardiomyocytes, lipids are stored in lipid droplets (LDs) and are utilized in mitochondria, although the structural and functional connections between these two organelles remain largely unknown. In this study, visible evidence have presented indicating that a complex is formed at the mitochondria-LD membrane contact (MLC) site, involving mitochondrion-localized Mfn2 and LD-localized Hsc70. This complex serves to tether mitochondria to LDs, facilitating the transfer of fatty acids (FAs) from LDs to mitochondria for β-oxidation. Reduction of Mfn2 induced by lipid overload inhibits MLC, hinders FA transfer, and results in lipid accumulation. Restoring Mfn2 reinstates MLC, alleviating myocardial lipotoxicity under lipid overload conditions both in-vivo and in-vitro. Additionally, prolonged lipid overload induces Mfn2 degradation through the ubiquitin-proteasome pathway, following Mfn2 acetylation at the K243 site. This leads to the transition from adaptive lipid utilization to maladaptive lipotoxicity. The experimental findings are supported by clinical data from patients with obesity and age-matched non-obese individuals. These translational results make a significant contribution to the molecular understanding of MLC in the heart, and offer new insights into its role in myocardial lipotoxicity.
    Keywords:  Hsc70; Mfn2; lipid overload; mitochondrion-lipid droplets membrane contacts; myocardial lipotoxicity
    DOI:  https://doi.org/10.1002/advs.202307749
  9. J Comp Neurol. 2024 Feb;532(2): e25575
    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 are 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:  Kv2.1; Kv2.2; dorsal root ganglion; somatosensory neurons; voltage-gated ion channels
    DOI:  https://doi.org/10.1002/cne.25575
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