bims-mitdyn 2020-07-13 papers

Sci Adv. 2020 Jun;6(26): eaaz9805

Lysosomal recycling of amino acids affects ER quality control.

Recent work has highlighted the fact that lysosomes are a critical signaling hub of metabolic processes, providing fundamental building blocks crucial for anabolic functions. How lysosomal functions affect other cellular compartments is not fully understood. Here, we find that lysosomal recycling of the amino acids lysine and arginine is essential for proper ER quality control through the UPRER. Specifically, loss of the lysine and arginine amino acid transporter LAAT-1 results in increased sensitivity to proteotoxic stress in the ER and decreased animal physiology. We find that these LAAT-1-dependent effects are linked to glycine metabolism and transport and that the loss of function of the glycine transporter SKAT-1 also increases sensitivity to ER stress. Direct lysine and arginine supplementation, or glycine supplementation alone, can ameliorate increased ER stress sensitivity found in laat-1 mutants. These data implicate a crucial role in recycling lysine, arginine, and glycine in communication between the lysosome and ER.

DOI: https://doi.org/10.1126/sciadv.aaz9805

Nature. 2020 Jul;583(7815): E19-E20

Reply to: In vivo quantification of mitochondrial membrane potential.

Milica Momcilovic, Orian Shirihai, Michael P Murphy, Carla M Koehler, Saman Sadeghi, David B Shackelford.

DOI: https://doi.org/10.1038/s41586-020-2367-9

Cells. 2020 Jul 07. pii: E1637. [Epub ahead of print]9(7):

Chemical Modulation of Mitochondria-Endoplasmic Reticulum Contact Sites.

Ana Paula Magalhães Rebelo, Federica Dal Bello, Tomas Knedlik, Natasha Kaar, Fabio Volpin, Sang Hun Shin, Marta Giacomello.

Contact sites between mitochondria and endoplasmic reticulum (ER) are points in which the two organelles are in close proximity. Due to their structural and functional complexity, their exploitation as pharmacological targets has never been considered so far. Notwithstanding, the number of compounds described to target proteins residing at these interfaces either directly or indirectly is rising. Here we provide original insight into mitochondria-ER contact sites (MERCs), with a comprehensive overview of the current MERCs pharmacology. Importantly, we discuss the considerable potential of MERCs to become a druggable target for the development of novel therapeutic strategies.

Keywords: cancer; diabetes; drug targets; mitochondria-associated membranes; mitochondria–endoplasmic reticulum contact sites; neurodegeneration; pharmacology; synthetic and biological compounds

DOI: https://doi.org/10.3390/cells9071637

Nat Cell Biol. 2020 Jul 08.

Protein homeostasis from the outside in.

Brant M Webster, Holly K Gildea, Andrew Dillin.

DOI: https://doi.org/10.1038/s41556-020-0534-8

Front Cell Dev Biol. 2020 ;8 428

Endoplasmic Reticulum-Mitochondria Contact Sites and Neurodegeneration.

Lingna Xu, Xi Wang, Chao Tong.

Endoplasmic reticulum-mitochondria contact sites (ERMCSs) are dynamic contact regions with a distance of 10-30 nm between the endoplasmic reticulum and mitochondria. Endoplasmic reticulum-mitochondria contact sites regulate various biological processes, including lipid transfer, calcium homeostasis, autophagy, and mitochondrial dynamics. The dysfunction of ERMCS is closely associated with various neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis. In this review, we will summarize the current knowledge of the components and organization of ERMCSs, the methods for monitoring ERMCSs, and the physiological functions of ERMCSs in different model systems. Additionally, we will emphasize the current understanding of the malfunction of ERMCSs and their potential roles in neurodegenerative diseases.

Keywords: autophagy; contact sites; endoplasmic reticulum; mitochdonrion; neurodegeneration

DOI: https://doi.org/10.3389/fcell.2020.00428

Elife. 2020 Jul 10. pii: e56584. [Epub ahead of print]9

Miga mediated endoplasmic reticulum-mitochondria contact sites regulate neuronal homeostasis.

Lingna Xu, Xi Wang, Jia Zhou, Yunyi Qiu, Weina Shang, Jun-Ping Liu, Liquan Wang, Chao Tong.

Endoplasmic reticulum (ER)-mitochondria contact sites (ERMCSs) are crucial for multiple cellular processes such as calcium signaling, lipid transport, mitochondrial dynamics, and autophagosome biogenesis. However, the molecular organization, functions, and regulation of ERMCS are not fully understood in higher eukaryotes. Also, the physiological roles of altered ERMCSs are not well defined. In this study, we found that Miga, a mitochondrion located protein, markedly increases ERMCSs and causes severe neurodegeneration upon overexpression in fly eyes. Miga interacts with an ER protein Vap33 through its FFAT-like motif and an amyotrophic lateral sclerosis (ALS) disease related Vap33 mutation considerably reduces its interaction with Miga. Multiple serine residues inside and near the Miga FFAT motif were phosphorylated, which is required for its interaction with Vap33 and Miga mediated ERMCS formation. The interaction between Vap33 and Miga promoted further phosphorylation of upstream serine/threonine clusters, which fine-tuned Miga activity. Protein kinases CKI and CaMKII contribute to Miga hyperphosphorylation. MIGA2, encoded by the miga mammalian ortholog, has conserved functions in mammalian cells. We propose a model that shows Miga interacts with Vap33 to mediate ERMCSs and excessive ERMCSs lead to neurodegeneration.

Keywords: D. melanogaster; cell biology; human

DOI: https://doi.org/10.7554/eLife.56584

Aging Cell. 2020 Jul 06. e13187

Aging is associated with a decline in Atg9b-mediated autophagosome formation and appearance of enlarged mitochondria in the heart.

Wenjing Liang, Alexandra G Moyzis, Mark A Lampert, Rachel Y Diao, Rita H Najor, Åsa B Gustafsson.

Advancing age is a major risk factor for developing heart disease, and the biological processes contributing to aging are currently under intense investigation. Autophagy is an important cellular quality control mechanism that is reduced in tissues with age but the molecular mechanisms underlying the age-associated defects in autophagy remain poorly characterized. Here, we have investigated how the autophagic process is altered in aged mouse hearts. We report that autophagic activity is reduced in aged hearts due to a reduction in autophagosome formation. Gene expression profile analysis to evaluate changes in autophagy regulators uncovered a reduction in Atg9b transcript and protein levels. Atg9 proteins are critical in delivering membrane to the growing autophagosome, and siRNA knockdown of Atg9b in cells confirmed a reduction in autophagosome formation. Autophagy is also the main pathway involved in eliminating dysfunctional mitochondria via a process known as mitophagy. The E3 ubiquitin ligase Parkin plays a key role in labeling mitochondria for mitophagy. We also found increased levels of Parkin-positive mitochondria in the aged hearts, an indication that they have been labeled for mitophagy. In contrast, Nrf1, a major transcriptional regulator of mitochondrial biogenesis, was significantly reduced in aged hearts. Additionally, our data showed reduced Drp1-mediated mitochondrial fission and formation of enlarged mitochondria in the aged heart. Overall, our findings suggest that cardiac aging is associated with reduced autophagosome number, decreased mitochondrial turnover, and formation of megamitochondria.

Keywords: Atg9; Parkin; aging; autophagy; heart; mitochondria; mitophagy

DOI: https://doi.org/10.1111/acel.13187