bims-mecosi 2023-01-01 papers

Issue of 2023–01–01
three papers selected by
Verena Kohler, University of Graz

Cell Mol Neurobiol. 2022 Dec 26.

Alzheimer's-Associated Upregulation of Mitochondria-Associated ER Membranes After Traumatic Brain Injury.

Rishi R Agrawal, Delfina Larrea, Yimeng Xu, Lingyan Shi, Hylde Zirpoli, Leslie G Cummins, Valentina Emmanuele, Donghui Song, Taekyung D Yun, Frank P Macaluso, Wei Min, Steven G Kernie, Richard J Deckelbaum, Estela Area-Gomez.

Traumatic brain injury (TBI) can lead to neurodegenerative diseases such as Alzheimer's disease (AD) through mechanisms that remain incompletely characterized. Similar to AD, TBI models present with cellular metabolic alterations and modulated cleavage of amyloid precursor protein (APP). Specifically, AD and TBI tissues display increases in amyloid-β as well as its precursor, the APP C-terminal fragment of 99 a.a. (C99). Our recent data in cell models of AD indicate that C99, due to its affinity for cholesterol, induces the formation of transient lipid raft domains in the ER known as mitochondria-associated endoplasmic reticulum (ER) membranes ("MAM" domains). The formation of these domains recruits and activates specific lipid metabolic enzymes that regulate cellular cholesterol trafficking and sphingolipid turnover. Increased C99 levels in AD cell models promote MAM formation and significantly modulate cellular lipid homeostasis. Here, these phenotypes were recapitulated in the controlled cortical impact (CCI) model of TBI in adult mice. Specifically, the injured cortex and hippocampus displayed significant increases in C99 and MAM activity, as measured by phospholipid synthesis, sphingomyelinase activity and cholesterol turnover. In addition, our cell type-specific lipidomics analyses revealed significant changes in microglial lipid composition that are consistent with the observed alterations in MAM-resident enzymes. Altogether, we propose that alterations in the regulation of MAM and relevant lipid metabolic pathways could contribute to the epidemiological connection between TBI and AD.

Keywords: Alzheimer’s; Brain injury; Contact sites; Lipids; Mitochondria; Neurodegeneration

DOI: https://doi.org/10.1007/s10571-022-01299-0

Contact (Thousand Oaks). 2022 Jan;5 251525642211343

Sequence Analysis and Structural Predictions of Lipid Transfer Bridges in the Repeating Beta Groove (RBG) Superfamily Reveal Past and Present Domain Variations Affecting Form, Function and Interactions of VPS13, ATG2, SHIP164, Hobbit and Tweek.

Tim P Levine.

Lipid transfer between organelles requires proteins that shield the hydrophobic portions of lipids as they cross the cytoplasm. In the last decade a new structural form of lipid transfer protein (LTP) has been found: long hydrophobic grooves made of beta-sheet that bridge between organelles at membrane contact sites. Eukaryotes have five families of bridge-like LTPs: VPS13, ATG2, SHIP164, Hobbit and Tweek. These are unified into a single superfamily through their bridges being composed of just one domain, called the repeating beta groove (RBG) domain, which builds into rod shaped multimers with a hydrophobic-lined groove and hydrophilic exterior. Here, sequences and predicted structures of the RBG superfamily were analyzed in depth. Phylogenetics showed that the last eukaryotic common ancestor contained all five RBG proteins, with duplicated VPS13s. The current set of long RBG protein appears to have arisen in even earlier ancestors from shorter forms with 4 RBG domains. The extreme ends of most RBG proteins have amphipathic helices that might be an adaptation for direct or indirect bilayer interaction, although this has yet to be tested. The one exception to this is the C-terminus of SHIP164, which instead has a coiled-coil. Finally, the exterior surfaces of the RBG bridges are shown to have conserved residues along most of their length, indicating sites for partner interactions almost all of which are unknown. These findings can inform future cell biological and biochemical experiments.

Keywords: BLTP1; BLTP2; CLANS; ColabFold; Csf1; Fmp27; HHpred; UHRF1BP1L; UHRFBLP1L; Ypr117w

DOI: https://doi.org/10.1177/25152564221134328

Xi Bao Yu Fen Zi Mian Yi Xue Za Zhi. 2022 Dec;38(12): 1104-1110

[Dithiothreitol promotes apoptosis in rat hepatocytes by inhibiting family with sequence similarity 134 member B (FAM134B)-mediated endoplasmic reticulophagy].

Yixin Guo, Bing Han, Ting Yang, Yusi Chen, Yi Yang, Cai Liang, Jiayao Li, Qin Yang, Rujia Xie.

Objective To investigate the effect of family with sequence similarity 134 member B (FAM134B)-mediated endoplasmic reticulophagy on apoptosis of hepatocytes induced by endoplasmic reticulum stress (ERS) and identify its potential regulatory mechanism. Methods BRL-3A cells were treated with 0, 0.5, 1.0, 2.0, 4.0, 6.0 mmol/L dithiothreitol (DTT) for 48 hours. The effect of DTT treatment on the proliferation and apoptosis was analyzed using real time cellular dynamic analysis (RTCA) and flow cytometry. The level of proteins related to ERS, endoplasmic reticulophagy, mitochondria-endoplasmic reticulum contact sites (MERCs), and mitochondrial apoptosis pathway were determined using Western blot analysis. Co-localization of ER and lysosomes were detected using ER and lysosomal fluorescence probes. A Ca2+ fluorescence probe was used to detect the level of Ca2+ in mitochondria. Results DTT treatment significantly inhibited cell proliferation and promoted apoptosis in hepatocytes. The levels of proteins related to ERS and endoplasmic reticulophagy, MERCs and the mitochondrial apoptosis pathway significantly increased in BRL-3A cells treated with DTT. DTT treatment decreased the ER-lysosome co-localization and enhanced the fluorescence intensity of Ca2+ in mitochondria. Conclusion DTT aggravates hepatocyte apoptosis by inhibiting FAM134B-mediated endoplasmic reticulophagy and enhancing the level of mitochondrial Ca2+.