bims-mitper 2023-02-05 papers

Issue of 2023‒02‒05
six papers selected by
Bradley Irizarry
Thomas Jefferson University

Methods Cell Biol. 2023 ;pii: S0091-679X(22)00143-1. [Epub ahead of print]174 93-111

Quantitative assessment of mitophagy in irradiated cancer cells.

Emma Guilbaud, Sheila Spada, Norma Bloy, Claudia Galassi, Ai Sato, Carlos Jiménez-Cortegana, Artur Aretz, Aitziber Buqué, Takahiro Yamazaki, Sandra Demaria, Lorenzo Galluzzi.

Mitophagy is a finely regulated mechanism through which eukaryotic cells selectively dispose of supernumerary, permeabilized or otherwise damaged mitochondria through lysosomal degradation. Dysfunctional mitochondria are prone to release potentially cytotoxic factors including reactive oxygen species (ROS) and caspase activators, such as cytochrome c, somatic (CYCS). Thus, proficient mitophagic responses mediate prominent cytoprotective functions. Moreover, the rapid degradation of permeabilized mitochondria limits the release of mitochondrial components that may drive inflammatory reactions, such as mitochondrial DNA (mtDNA) and transcription factor A, mitochondrial (TFAM), implying that mitophagy also mediates potent anti-inflammatory effects. Here, we detail a simple, flow cytometry-assisted protocol for the specific measurement of mitophagic responses as driven by radiation therapy (RT) in mouse hormone receptor (HR)+ mammary carcinoma TS/A cells. With some variations, this method - which relies on the mitochondria-restricted expression of a fluorescent reporter that is sensitive to pH and hence changes excitation wavelength within lysosomes (mt-mKeima) - can be adapted to a variety of human and mouse cancer cell lines and/or straightforwardly implemented on fluorescence microscopy platforms.

Keywords: Antimycin; Autophagy; CGAS/STING1; NLRP3 inflammasome; Oligomycin; PRKN; SARRP

DOI: https://doi.org/10.1016/bs.mcb.2022.09.002

PNAS Nexus. 2022 Sep;1(4): pgac192

An explanation of how mutant and wild-type mitochondria might stably co-exist in inherited mitochondrial diseases.

Axel Kowald, Felix P Kemeth, Tom B L Kirkwood.

Mitochondria are cellular organelles of crucial relevance for the survival of metazoan organisms. Damage to the mitochondrial DNA can give rise to a variety of mitochondrial diseases and is thought also to be involved in the aging process. The fate of mtDNA mutants is controlled by their synthesis as well as degradation and mathematical models can help to better understand this complex interplay. We present here a model that combines a replicative advantage for mtDNA mutants with selective degradation enabled by mitochondrial fission and fusion processes. The model not only shows that the cell has efficient means to deal with (many) types of mutants but, surprisingly, also predicts that under certain conditions a stable co-existence of mutant and wild-type mtDNAs is possible. We discuss how this new finding might explain how mitochondria can be at the heart of processes with such different phenotypes as mitochondrial diseases and aging.

Keywords: aging; mathematical model; mitochondrial disease

DOI: https://doi.org/10.1093/pnasnexus/pgac192

J Toxicol Sci. 2023 ;48(2): 65-73

Lipopolysaccharide administration increases the susceptibility of mitochondrial permeability transition pore opening via altering adenine nucleotide translocase conformation in the mouse liver.

Ryota Nakajima, Akinori Takemura, Yugo Ikeyama, Kousei Ito.

Lipopolysaccharide (LPS), a component of the outer membrane of gram-negative bacteria, induces various biological reactions in vivo. Our previous study suggested that LPS administration disrupts respiratory chain complex activities, enhances reactive oxygen species production, especially in the liver mitochondria, and sensitizes mitochondrial permeability transition (MPT) pore opening in rats. However, it is unknown whether LPS-induced MPT pore opening in rats is similarly observed in mice and whether the mechanism is the same. LPS administration to mice increased not only cyclosporin A-sensitive swelling (MPT pore opening) susceptibility, but also induced cyclosporin A-insensitive basal swelling, unlike in rats. In addition, respiratory activity observed after adding ADP was significantly decreased. Based on these results, we further investigated the role of adenine nucleotide translocase (ANT). Carboxyatractyloside (CATR; an ANT inhibitor) treatment decreased respiratory activity after ADP was added in vehicle-treated mitochondria similarly to LPS administration. Additionally, CATR treatment increased MPT pore opening susceptibility in LPS-treated mitochondria compared to that of vehicle-treated mitochondria. Our study shows that ANT maintained a c-state conformation upon LPS administration, which increased MPT pore opening susceptibility in mice. These results suggest that LPS enhances MPT pore opening susceptibility across species, but the mechanism may differ between rat and mouse.

Keywords: Adenine nucleotide translocase; Animal species difference; Lipopolysaccharide; Mitochondria; Mitochondrial permeability transition

DOI: https://doi.org/10.2131/jts.48.65

Sci China Life Sci. 2023 Feb 03.

Innate and adaptive immune abnormalities underlying autoimmune diseases: the genetic connections.

Xinxin Chi, Miaozhen Huang, Hailin Tu, Bin Zhang, Xin Lin, Huji Xu, Chen Dong, Xiaoyu Hu.

With the exception of an extremely small number of cases caused by single gene mutations, most autoimmune diseases result from the complex interplay between environmental and genetic factors. In a nutshell, etiology of the common autoimmune disorders is unknown in spite of progress elucidating certain effector cells and molecules responsible for pathologies associated with inflammatory and tissue damage. In recent years, population genetics approaches have greatly enriched our knowledge regarding genetic susceptibility of autoimmunity, providing us with a window of opportunities to comprehensively re-examine autoimmunity-associated genes and possible pathways. In this review, we aim to discuss etiology and pathogenesis of common autoimmune disorders from the perspective of human genetics. An overview of the genetic basis of autoimmunity is followed by 3 chapters detailing susceptibility genes involved in innate immunity, adaptive immunity and inflammatory cell death processes respectively. With such attempts, we hope to expand the scope of thinking and bring attention to lesser appreciated molecules and pathways as important contributors of autoimmunity beyond the 'usual suspects' of a limited subset of validated therapeutic targets.

Keywords: adaptive immunity; autoimmune diseases; etiology; innate immunity; pathogenesis

DOI: https://doi.org/10.1007/s11427-021-2187-3

Bioessays. 2023 Jan 29. e2200160

Mitochondrial protein import machinery conveys stress signals to the cytosol and beyond.

Eirini Lionaki, Ilias Gkikas, Nektarios Tavernarakis.

Mitochondria hold diverse and pivotal roles in fundamental processes that govern cell survival, differentiation, and death, in addition to organismal growth, maintenance, and aging. The mitochondrial protein import system is a major contributor to mitochondrial biogenesis and lies at the crossroads between mitochondrial and cellular homeostasis. Recent findings highlight the mitochondrial protein import system as a signaling hub, receiving inputs from other cellular compartments and adjusting its function accordingly. Impairment of protein import, in a physiological, or disease context, elicits adaptive responses inside and outside mitochondria. In this review, we discuss recent developments, relevant to the mechanisms of mitochondrial protein import regulation, with a particular focus on quality control, proteostatic and metabolic cellular responses, triggered upon impairment of mitochondrial protein import.

Keywords: metabolism; mitochondrial protein import; mitochondrial unfolded protein response; mitophagy; proteostasis

DOI: https://doi.org/10.1002/bies.202200160