bims-mitlys Biomed News
on Mitochondria and Lysosomes
Issue of 2021‒06‒13
five papers selected by
Nicoletta Plotegher
University of Padua

  1. Proc Natl Acad Sci U S A. 2021 Jun 15. pii: e2020078118. [Epub ahead of print]118(24):
      Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disease characterized by myelin damage followed by axonal and ultimately neuronal loss. The etiology and physiopathology of MS are still elusive, and no fully effective therapy is yet available. We investigated the role in MS of autophagy (physiologically, a controlled intracellular pathway regulating the degradation of cellular components) and of mitophagy (a specific form of autophagy that removes dysfunctional mitochondria). We found that the levels of autophagy and mitophagy markers are significantly increased in the biofluids of MS patients during the active phase of the disease, indicating activation of these processes. In keeping with this idea, in vitro and in vivo MS models (induced by proinflammatory cytokines, lysolecithin, and cuprizone) are associated with strongly impaired mitochondrial activity, inducing a lactic acid metabolism and prompting an increase in the autophagic flux and in mitophagy. Multiple structurally and mechanistically unrelated inhibitors of autophagy improved myelin production and normalized axonal myelination, and two such inhibitors, the widely used antipsychotic drugs haloperidol and clozapine, also significantly improved cuprizone-induced motor impairment. These data suggest that autophagy has a causal role in MS; its inhibition strongly attenuates behavioral signs in an experimental model of the disease. Therefore, haloperidol and clozapine may represent additional therapeutic tools against MS.
    Keywords:  antipsychotic drugs; autophagy; mitochondria; multiple sclerosis; remyelination
  2. Front Cell Dev Biol. 2021 ;9 653828
      It has become apparent that our textbook illustration of singular isolated organelles is obsolete. In reality, organelles form complex cooperative networks involving various types of organelles. Light microscopic and ultrastructural studies have revealed that mitochondria-endoplasmic reticulum (ER) contact sites (MERCSs) are abundant in various tissues and cell types. Indeed, MERCSs have been proposed to play critical roles in various biochemical and signaling functions such as Ca2+ homeostasis, lipid transfer, and regulation of organelle dynamics. While numerous proteins involved in these MERCS-dependent functions have been reported, how they coordinate and cooperate with each other has not yet been elucidated. In this review, we summarize the functions of mammalian proteins that localize at MERCSs and regulate their formation. We also discuss potential roles of the MERCS proteins in regulating multiple organelle contacts.
    Keywords:  ER; mammalian protein; mitochondria; organelle contact sites; tether
  3. Methods Mol Biol. 2021 ;2275 363-378
      In the last decades, membrane contact sites (MCSs) have been the object of intense investigation in different fields of cell physiology and pathology and their importance for the correct functioning of the cell is now widely recognized. MCS between any known intercellular organelles, including endoplasmic reticulum (ER), mitochondria, Golgi, endosomes, peroxisomes, lysosomes, lipid droplets, and the plasma membrane (PM), have been largely documented and in some cases the molecules responsible for the tethering also identified. They represent specific membrane hubs where a tightly coordinated exchange of ions, lipids, nutrients, and factors required to maintain proper cellular homeostasis takes place. Their delicate, dynamic, and sometimes elusive nature prevented and/or delayed the development of tools to easily image interorganelle proximity under physiological conditions and in living organisms. Nowadays, this aspect received great momentum due to the finding that MCSs' dysregulation is involved in several pathological conditions. We have recently developed modular, split-GFP-based contact site sensors (SPLICS) engineered to fluoresce when homo- and heterotypic juxtapositions between ER and mitochondria occur over a range of specific distances. Here we describe in detail, by highlighting strengths and weaknesses, the use and the application of these novel genetically encoded SPLICS sensors and how to properly quantify short- and long-range ER-mitochondria interactions.
    Keywords:  ER–Mitochondria tethering; Endoplasmic reticulum; Mitochondria; Organelle contact sites; SPLICS; Split GFP
  4. Contact (Thousand Oaks). 2020 Jan 01. 3 1-13
      Lipid droplets (LDs) are dynamic fat-storage organelles that interact readily with numerous cellular structures and organelles. A prominent LD contact site is with degradative vesicles such as autophagosomes, lysosomes, autolysosomes, and late endosomes. These contacts support lipid catabolism through the selective autophagy of LDs (i.e., lipophagy) or the recruitment of cytosolic lipases to the LD surface (i.e., lipolysis). However, LD-autophagosome contacts serve additional functions beyond lipid catabolism, including the supply of lipids for autophagosome biogenesis. In this review, we discuss the molecular mediators of LD contacts with autophagosomes and other degradative organelles as well as the diverse cellular functions of these contact sites in health and disease.
    Keywords:  autophagosome; autophagy; cell biology; endosome; lipid droplet; lysosome
  5. Am J Physiol Cell Physiol. 2021 06 09.
      Maintaining mitochondrial function and dynamics is crucial for cellular health. In muscle, defects in mitochondria result in severe myopathies where accumulation of damaged mitochondria causes deterioration and dysfunction. Importantly, understanding the role of mitochondria in disease is a necessity to determine future therapeutics. One of the most common myopathies is mitochondrial encephalopathy lactic acidosis stroke-like episodes (MELAS), which has no current treatment. Recently, MELAS patients treated with rapamycin exhibited improved clinical outcomes. However, the cellular mechanisms of rapamycin effects in MELAS patients are currently unknown. In this study, we used cultured skin fibroblasts as a window into the mitochondrial dysfunction evident in MELAS cells, as well as to study the mechanisms of rapamycin action, compared to control, healthy individuals. We observed that mitochondria from patients were fragmented, had a 3-fold decline in the average speed of motility, a 2-fold reduced mitochondrial membrane potential and a 1.5-2-fold decline in basal respiration. Despite the reduction in mitochondrial function, mitochondrial import protein Tim23 was elevated in patient cell lines. MELAS fibroblasts exhibited increased MnSOD levels and lysosomal function when compared to healthy controls. Treatment of MELAS fibroblasts with rapamycin for 24 hrs resulted in increased mitochondrial respiration compared to control cells, a higher lysosome content, and a greater localization of mitochondria to lysosomes. Our studies suggest that rapamycin has the potential to improve cellular health even in the presence of mtDNA defects, primarily via an increase in lysosomal content.
    Keywords:  human fibroblasts; lysosomes; mitochondrial health; mitochondrial myopathies