bims-mikwok 2022-09-25 papers

Issue of 2022–09–25
five papers selected by
Avinash N. Mukkala, University of Toronto

JCI Insight. 2022 Sep 22. pii: e159286. [Epub ahead of print]7(18):

Flow pattern-dependent mitochondrial dynamics regulates the metabolic profile and inflammatory state of endothelial cells.

Soon-Gook Hong, Junchul Shin, Soo Young Choi, Jeffery C Powers, Benjamin M Meister, Jacqueline Sayoc, Jun Seok Son, Ryan Tierney, Fabio A Recchia, Michael D Brown, Xiaofeng Yang, Joon-Young Park.

Endothelial mitochondria play a pivotal role in maintaining endothelial cell (EC) homeostasis through constantly altering their size, shape, and intracellular localization. Studies show that the disruption of the basal mitochondrial network in EC, forming excess fragmented mitochondria, implicates cardiovascular disease. However, cellular consequences underlying the morphological changes in the endothelial mitochondria under distinctively different, but physiologically occurring, flow patterns (i.e., unidirectional flow [UF] versus disturbed flow [DF]) are largely unknown. The purpose of this study was to investigate the effect of different flow patterns on mitochondrial morphology and its implications in EC phenotypes. We show that mitochondrial fragmentation is increased at DF-exposed vessel regions, where elongated mitochondria are predominant in the endothelium of UF-exposed regions. DF increased dynamin-related protein 1 (Drp1), mitochondrial reactive oxygen species (mtROS), hypoxia-inducible factor 1, glycolysis, and EC activation. Inhibition of Drp1 significantly attenuated these phenotypes. Carotid artery ligation and microfluidics experiments further validate that the significant induction of mitochondrial fragmentation was associated with EC activation in a Drp1-dependent manner. Contrarily, UF in vitro or voluntary exercise in vivo significantly decreased mitochondrial fragmentation and enhanced fatty acid uptake and OXPHOS. Our data suggest that flow patterns profoundly change mitochondrial fusion/fission events, and this change contributes to the determination of proinflammatory and metabolic states of ECs.

Keywords: Atherosclerosis; Endothelial cells; Mitochondria; Vascular Biology

DOI: https://doi.org/10.1172/jci.insight.159286

EMBO Rep. 2022 Sep 20. e54910

Functional platelet-derived mitochondria induce the release of human neutrophil microvesicles.

Jacob L Léger, Marie-France N Soucy, Vanessa Veilleux, Robert D Foulem, Gilles A Robichaud, Marc E Surette, Eric P Allain, Luc H Boudreau.

Inflammation is an essential process of host defense against infections, illness, or tissue damage. Polymorphonuclear neutrophils (PMN) are among the first immune cells involved in acute inflammatory responses and are on the front line in the fight against bacterial infections. In the presence of bacterial fragments, PMN release inflammatory mediators, enzymes, and microvesicles in the extracellular milieu to recruit additional immune cells required to eliminate the pathogens. Recent evidence shows that platelets (PLTs), initially described for their role in coagulation, are involved in inflammatory responses. Furthermore, upon activation, PLT also release functional mitochondria (freeMitos) within their extracellular milieu. Mitochondria share characteristics with bacterial and mitochondrial damage-associated molecular patterns, which are important contributors in sterile inflammation processes. Deep sequencing transcriptome analysis demonstrates that freeMitos increase the mitochondrial gene expression in PMN. However, freeMitos do not affect the mitochondrial-dependent increase in oxygen consumption in PMN. Interestingly, freeMitos significantly induce the release of PMN-derived microvesicles. This study provides new insight into the role of freeMitos in the context of sterile inflammation.

Keywords: extracellular vesicles; freeMitos; sterile inflammation

DOI: https://doi.org/10.15252/embr.202254910

J Clin Invest. 2022 Sep 20. pii: e161638. [Epub ahead of print]

A Mitofusin 2 - Hif1α axis sets a maturation checkpoint in regenerating skeletal muscle.

Xun Wang, Yuemeng Jia, Jiawei Zhao, Nicholas P Lesner, Cameron J Menezes, Spencer D Shelton, Siva Sai Krishna Venigalla, Jian Xu, Chunyu Cai, Prashant Mishra.

A fundamental issue in regenerative medicine is whether there exist endogenous regulatory mechanisms that limit the speed and efficiency of the repair process. We report the existence of a maturation checkpoint during muscle regeneration which pauses myofibers at a neonatal stage. This checkpoint is regulated by the mitochondrial protein mitofusin 2 (Mfn2), whose expression is activated in response to muscle injury. Mfn2 is required for growth and maturation of regenerating myofibers; in the absence of Mfn2, new myofibers arrested at a neonatal stage, characterized by centrally nucleated myofibers and loss of H3K27me3 repressive marks at the neonatal myosin heavy chain gene. A similar arrest at the neonatal stage was observed in infantile cases of human centronuclear myopathy. Mechanistically, Mfn2 upregulation suppressed expression of Hypoxia-induced Factor 1α (Hif1α), which is induced in the setting of muscle damage. Sustained Hif1α signaling blocked maturation of new myofibers at the neonatal-to-adult fate transition, revealing the existence of a checkpoint that delays muscle regeneration. Correspondingly, inhibition of Hif1α allowed myofibers to bypass the checkpoint, thereby accelerating the repair process. We conclude that skeletal muscle contains a regenerative checkpoint which regulates the speed of myofiber maturation in response to Mitofusin 2 and Hif1α activity.

Keywords: Epigenetics; Mitochondria; Muscle Biology; Stem cells

DOI: https://doi.org/10.1172/JCI161638

Nat Commun. 2022 Sep 22. 13(1): 5524

Endocytosis-like DNA uptake by cell wall-deficient bacteria.

Renée Kapteijn, Shraddha Shitut, Dennis Aschmann, Le Zhang, Marit de Beer, Deniz Daviran, Rona Roverts, Anat Akiva, Gilles P van Wezel, Alexander Kros, Dennis Claessen.

Horizontal gene transfer in bacteria is widely believed to occur via conjugation, transduction and transformation. These mechanisms facilitate the passage of DNA across the protective cell wall using sophisticated machinery. Here, we report that cell wall-deficient bacteria can engulf DNA and other extracellular material via an endocytosis-like process. Specifically, we show that L-forms of the filamentous actinomycete Kitasatospora viridifaciens can take up plasmid DNA, polysaccharides (dextran) and 150-nm lipid nanoparticles. The process involves invagination of the cytoplasmic membrane, leading to formation of intracellular vesicles that encapsulate extracellular material. DNA uptake is not affected by deletion of genes homologous to comEC and comEA, which are required for natural transformation in other species. However, uptake is inhibited by sodium azide or incubation at 4 °C, suggesting the process is energy-dependent. The encapsulated materials are released into the cytoplasm upon degradation of the vesicle membrane. Given that cell wall-deficient bacteria are considered a model for early life forms, our work reveals a possible mechanism for primordial cells to acquire food or genetic material before invention of the bacterial cell wall.

DOI: https://doi.org/10.1038/s41467-022-33054-w

Shock. 2022 Sep 01. 58(3): 231-235

NOT ALL CELL-FREE MITOCHONDRIAL DNA IS EQUAL IN TRAUMA PATIENTS.

Gabrielle D Briggs, Scott Gelzinnis, Simone Meakes, Kate L King, Zsolt J Balogh.

ABSTRACT: Mitochondrial DNA (mtDNA) acts as a proinflammatory damage-associated molecular pattern that stimulates innate immune activation via Toll-like receptor 9, similarly to bacterial DNA. A number of clinical studies have measured elevated cell-free mtDNA in the plasma of trauma patients, thought to originate from tissue injury and inflammatory processes; however, the magnitude of this increase, the absolute concentration, and the association with poor outcomes varies considerably across studies. Measurements of cell-free mtDNA in healthy individuals have shown that the majority of "cell-free" mtDNA (>95%) can be centrifuged/filtered from plasma in the size range of 0.45 to 5 μm, suggesting that there are larger forms of mtDNA-containing complexes in the plasma that could be considered cell-free. Whether this is true for trauma patients (and other relevant disease states) and the clinical relevance of the larger forms of mtDNA is unknown. These findings from healthy individuals also suggest that the centrifugation speeds used to generate cell-free plasma (which are rarely consistent among studies) could result in mixed populations of cell-free mtDNA that could confound associations with outcomes. We demonstrate in this study of 25 major trauma patients that the majority of the cell-free mtDNA in trauma patient plasma (>95%) is removed after centrifugation at 16,000g. Despite the larger forms of mtDNA being predominant, they do not correlate with outcomes or expected parameters such as injury/shock severity, multiple organ failure, and markers of inflammation, whereas low-molecular-weight cell-free mtDNA correlates strongly with these variables.

DOI: https://doi.org/10.1097/SHK.0000000000001969