bims-mecosi 2024-11-10 papers

Issue of 2024–11–10
five papers selected by
Verena Kohler, Umeå University

Mol Metab. 2024 Nov 01. pii: S2212-8778(24)00187-X. [Epub ahead of print] 102056

TOMM40 regulates hepatocellular and plasma lipid metabolism via an LXR-dependent pathway.

Neil V Yang, Justin Y Chao, Kelly A Garton, Tommy Tran, Sarah M King, Joseph Orr, Jacob H Oei, Alexandra Crawford, Misun Kang, Reena Zalpuri, Danielle M Jorgens, Pranav Konchadi, John S Chorba, Elizabeth Theusch, Ronald M Krauss.

The gene encoding TOMM40 (Transporter of Outer Mitochondrial Membrane 40) is adjacent to that encoding APOE, which has a central role in lipid and lipoprotein metabolism. Human genetic variants near APOE and TOMM40 are strongly associated with plasma lipid levels, but a specific role for TOMM40 in lipid metabolism has not been established. We show here that suppression of TOMM40 in human hepatoma cells upregulates expression of APOE and LDLR in part via activation of LXRB (NR1H2) by oxysterols, with consequent increased uptake of VLDL and LDL. This is in part due to disruption of mitochondria-endoplasmic reticulum contact sites, with resulting accrual of reactive oxygen species and non-enzymatically derived oxysterols. With TOMM40 knockdown, cellular triglyceride and lipid droplet content are increased, effects attributable in part to receptor-mediated VLDL uptake, since lipid staining is significantly reduced by concomitant suppression of either LDLR or APOE. In contrast, cellular cholesterol content is reduced due to LXRB-mediated upregulation of the ABCA1 transporter as well as increased production and secretion of oxysterol-derived cholic acid. Consistent with the findings in hepatoma cells, in vivo knockdown of TOMM40 in mice results in significant reductions of plasma triglyceride and cholesterol concentrations, reduced hepatic cholesterol and increased triglyceride content, and accumulation of lipid droplets leading to development of steatosis. These findings demonstrate a role for TOMM40 in regulating hepatic lipid and plasma lipoprotein levels and identify mechanisms linking mitochondrial function with lipid metabolism.

DOI: https://doi.org/10.1016/j.molmet.2024.102056

Methods Enzymol. 2024 ;pii: S0076-6879(24)00381-1. [Epub ahead of print]707 153-171

Analysis of protein trafficking between mitochondria and the endoplasmic reticulum by fluorescence microscopy.

Shunsuke Matsumoto, Suzuka Ono, Toshiya Endo.

Precise protein localization is essential for normal cellular functions. However, recent studies have revealed that protein targeting is error-prone, and tail-anchored proteins mistargeted to mitochondria are transferred to the endoplasmic reticulum (ER) by an ATPase Msp1 (yeast)/ATAD1 (human) in the mitochondrial outer membrane for further quality examination in the ER to determine their fate, degradation or re-targeting. Analysis of the inter-organelle transfer of proteins requires a combination of time-lapse fluorescence microscopy and a system to achieve regulation of the protein levels of both transfer substrates and factors regulating the transfer in a coordinated manner at precise timing. This can be achieved by using a promoter switch for expression and acute depletion of involved factors through the degron-based proteasome system. In this chapter, we will describe methods to analyze inter-organelle protein transfer by fluorescence microscope within living yeast cells, by using the example of Msp1-mediated transfer of mistargeted proteins from mitochondria to the ER.

Keywords: AID degradation system; Endoplasmic reticulum; Fluorescence microscope; GET system; Inter-organelle protein transfer; Mitochondria; Msp1; Tail-anchored protein

DOI: https://doi.org/10.1016/bs.mie.2024.07.041

ACS Infect Dis. 2024 Nov 05.

Apicomplexan Espionage: Orchestrated Miscommunication at the Host-Parasite Interface.

Vaisak Mohan, Sandeep Reddy Vinjamuri, Parnika Sahoo, Abhinav Hatwar, Sandra S N, Usha Krishna, Vyshnav P V, Kamalakannan Vijayan.

Intracellular parasites, including Toxoplasma and Plasmodium, are entirely reliant on the active scavenging of host-derived nutrients to fuel their replicative cycle, as they are confined within a specialized membrane-bound compartment, the parasitophorous vacuole (PV). Initial observations, based on the proximity of host vesicles to the parasitophorous vacuole membrane (PVM), suggested that parasites utilize host vesicles to obtain essential nutrients. However, mounting evidence has now unequivocally demonstrated that intracellular pathogens establish membrane contacts with host organelles, establishing control over host cellular machinery. These intimate interactions enable the parasites to gain unimpeded access to cytosolic resources critical for development while evading host immune responses. This review consolidates the latest advancements in understanding the molecular machinery driving these transkingdom contacts and their functional roles. Further investigation into these processes promises to revolutionize our understanding of organelle communication, with profound implications for identifying new therapeutic targets and strategies.

Keywords: Chlamydia; Membrane contact site; Plasmodium; Toxoplasma; host−pathogen interaction; nutrient scavenging

DOI: https://doi.org/10.1021/acsinfecdis.4c00526

Biochim Biophys Acta Mol Basis Dis. 2024 Oct 30. pii: S0925-4439(24)00540-4. [Epub ahead of print] 167546

Canine Mammary Tumours (CMTs) exploit mitochondrial cholesterol for aggressive reprogramming.

Liana Hardy, Brindha Kannan, Manuel Rigon, Genevieve Benton-Hawthorn, Renato L Previdelli, Iris M Reichler, Franco Guscetti, Mariusz P Kowalewski, Michelangelo Campanella.

In human breast cancer the mitochondrial translocator protein (TSPO) aids pro-survival cellular response by facilitating the formation of mitochondrial contact sites with the nucleus termed Nucleus Associated Mitochondria (NAM). Here, we show that TSPO positively associates with the aggressiveness of tissues and cells isolated from Canine Mammary Tumours (CMTs). TSPO is also readily upregulated in reprogrammed mammary tumour cells following long-term deprivation of oestrogen or exposure to the endocrine chemotherapeutic (ET) agent Tamoxifen. The latter triggers mitochondrial handling of cholesterol which is facilitated by TSPO whose upregulation reduces susceptibility to Tamoxifen. TSPO binding ligands boost, on the other hand, the efficacy of Tamoxifen and Chemotherapy agents. In aggressive canine mammary tumour cells, TSPO repression impairs the NF-kB pattern thus confirming the pro-survival role of the NAM uncovered in the human counterpart. Mitochondrial cholesterol handling via TSPO emerges therefore as a signature in the aggressive reprogramming of CMTs thus advancing our understanding of the molecular mechanisms underpinning this pathology. A novel target mechanism to improve bio-marking and therapeutic protocols is here proposed.

Keywords: Canine Mammary Tumours (CMTs); Cholesterol; Mitochondria; TSPO; Tamoxifene

DOI: https://doi.org/10.1016/j.bbadis.2024.167546

Methods Enzymol. 2024 ;pii: S0076-6879(24)00400-2. [Epub ahead of print]707 39-62

Monitoring α-helical membrane protein insertion into the outer mitochondrial membrane of yeast cells.

Isabelle Steymans, Thomas Becker.

Mitochondria are surrounded by two membranes, the outer and inner membrane. The outer membrane contains a few dozen integral membrane proteins that mediate transport, fusion and fission processes, form contact sites and are involved in signaling pathways. There are two different types of outer membrane proteins. A few proteins are membrane-integrated by a transmembrane β-barrel, while other proteins are embedded by single or multiple α-helical membrane segments. All outer membrane proteins are produced on cytosolic ribosomes, but their import mechanisms differ. The translocase of the outer mitochondrial membrane (TOM complex) and the sorting and assembly machinery (SAM complex) import β-barrel proteins. Different import pathways have been reported for proteins with α-helical membrane anchors. The mitochondrial import (MIM) complex is the major insertase for this type of proteins. The in vitro import of radiolabeled precursor proteins into isolated mitochondria is a versatile technique to study protein import into the outer mitochondrial membrane. The import of these proteins does not involve proteolytic processing and is not dependent on the membrane potential. Therefore, the import assay has to be combined with blue native electrophoresis, carbonate extraction or protease accessibility assays to determine the import efficiency. These techniques allow to define import steps, assembly intermediates and study membrane integration. The in vitro import assay has been a central tool to uncover specific import routes and mechanisms.

Keywords: MIM complex; Mitochondria; Protein sorting; SAM complex; TOM complex

DOI: https://doi.org/10.1016/bs.mie.2024.07.055