Ultrastructural features (bulges) of membrane nanotubes between cone-like photoreceptor cells: An investigation employing scanning electron microscopy

Membrane nanotubes (MNTs) are nanotubular cell-to-cell connections enabling cell-tocell signaling and cargo transfer. The presence of local MNT bulges has been reported by several studies. However, a detailed characterization ofMNT bulges concerning their geometrical properties has not been done yet. The aim of our study was to analyze MNT from cone-like photoreceptor cells (661 W) using scanning electron microscopy (SEM) in order to characterize MNT bulges, thereby increasing the knowledge of ultrastructural feature of MNTs. Our SEM analysis of two MNTs with multiple bulges revealed that (i) MNT bulges are characterized by a statistically significant local increase in the MNT diameter (125% and 250% for both MNTs analyzed), (ii) the thickness and length of the MNT bulges correspond to dimensions of mitochondria, peroxisomes and exosomes, and (iii) the MNT bulges seem not to be randomly distributed on the MNTs but exhibit a preferred spacing with a different median value for each MNT. Our findings highlight that the ultrastructure of MNT exhibits interesting properties that need to be further investigated. Introduction Nanotubular cell-to-cell connections termed “tunnelling nanotubes” or “membrane nanotubes” (MNTs) (the term used in this paper) enable diverse possibilities of cell-to-cell signaling and cargo transfer [1] [2] [3]. This includes the exchange of signal carriers (e.g. proteins), organelles (e.g. mitochondria), bacteria, viruses, exosomes, DNA, RNA, or electric long-range coupling [4] [5] [6] [7] [8]. The defining characteristics of MNTs are still being debated and the investigation of MNT properties is ongoing but recently a consensus of leading MNT researchers was published that MNTs can be defined as “tubular membrane connection between non-adjacent cells that allow direct intercellular communication, not necessarily gap junction-mediated”. MNTs also contain F-actin and/or tubulin, have a variable diameter of 50–800 nm and are open-ended [3]. It can be added that MNTs are filled with cytoplasm and have a lipid bilayer [9]. Some MNTs also contain microtubules [10] and have the gap junction protein Cx43 at the end [6]. In some cases, individual MNTs stick together to form a single, thicker, MNT [9]. As recently summarized by Rustom [11], MNTs are “intimately linked to the physiological state and pathological” state of cells and “represent a central joint element of diverse diseases, such as neurodegenerative disorders, diabetes or cancer”. Furthermore, MNTs seem to play an important role in long-range physical cell-to-cell signaling in multicellular organisms possibly enabling novel ways of physical signal transfer [12] and being involved in the functioning of neurosystems [13]. Studies have been published that report the existence of bulges, i.e. local increases of the diameter, of MNTs [14] [15] [16] [17] [6] [18] [19] [20] [21] [22]. This ultrastructural feature of MNTs was attributed to the presence of objects (vesicles or organelles) inside MNTs [6]. Objective Our objective was to document and analyze bulges of MNTs using scanning electron microscopy (SEM) to increase the knowledge of ultrastructural feature of MNTs. To our knowledge, a detailed characterization of MNT bulges concerning their geometrical Ultrastructural features (bulges) of membrane nanotubes between cone-like photoreceptor cells: An investigation employing scanning electron microscopy DOI: 10.19185/matters.201802000011 Matters (ISSN: 2297-8240) | 2 properties has not been done before.

[1]  H. Gaskins,et al.  Airyscan super‐resolution microscopy of mitochondrial morphology and dynamics in living tumor cells , 2018, Microscopy research and technique.

[2]  M. D. Den Boer,et al.  Tunneling Nanotubes and Gap Junctions–Their Role in Long-Range Intercellular Communication during Development, Health, and Disease Conditions , 2017, Front. Mol. Neurosci..

[3]  Kyle L Ellefsen,et al.  Lattice light sheet imaging of membrane nanotubes between human breast cancer cells in culture and in brain metastases , 2017, Scientific Reports.

[4]  K. Sahu,et al.  Macrophage conditioned medium induced cellular network formation in MCF‐7 cells through enhanced tunneling nanotube formation and tunneling nanotube mediated release of viable cytoplasmic fragments , 2017, Experimental cell research.

[5]  H. Lehmann,et al.  Depletion of Mitofusin-2 Causes Mitochondrial Damage in Cisplatin-Induced Neuropathy , 2017, Molecular Neurobiology.

[6]  Christopher J. Peddie,et al.  3D correlative light and electron microscopy of cultured cells using serial blockface scanning electron microscopy , 2017, Journal of Cell Science.

[7]  D. Freund,et al.  Tunneling nanotubes mediate the transfer of stem cell marker CD133 between hematopoietic progenitor cells. , 2016, Experimental hematology.

[8]  F. Scholkmann Long range physical cell-to-cell signalling via mitochondria inside membrane nanotubes: a hypothesis , 2016, Theoretical Biology and Medical Modelling.

[9]  A. Rustom The missing link: does tunnelling nanotube-based supercellularity provide a new understanding of chronic and lifestyle diseases? , 2016, Open Biology.

[10]  T. Wai,et al.  Mitochondrial Dynamics and Metabolic Regulation , 2016, Trends in Endocrinology & Metabolism.

[11]  Dianne Cox,et al.  Exosomes and nanotubes: Control of immune cell communication. , 2016, The international journal of biochemistry & cell biology.

[12]  H. Vaudry,et al.  Structural and functional analysis of tunneling nanotubes (TnTs) using gCW STED and gconfocal approaches , 2015, Biology of the cell.

[13]  F. Scholkmann Two emerging topics regarding long-range physical signaling in neurosystems: Membrane nanotubes and electromagnetic fields. , 2015, Journal of integrative neuroscience.

[14]  H. Gerdes,et al.  Transfer of mitochondria via tunneling nanotubes rescues apoptotic PC12 cells , 2015, Cell Death and Differentiation.

[15]  H. Tse,et al.  Mitochondrial transfer of induced pluripotent stem cell-derived mesenchymal stem cells to airway epithelial cells attenuates cigarette smoke-induced damage. , 2014, American journal of respiratory cell and molecular biology.

[16]  Huixia Lu,et al.  Mesenchymal stem cells rescue injured endothelial cells in an in vitro ischemia-reperfusion model via tunneling nanotube like structure-mediated mitochondrial transfer. , 2014, Microvascular research.

[17]  Jennifer J. Smith,et al.  Peroxisomes take shape , 2013, Nature Reviews Molecular Cell Biology.

[18]  You-yi Zhang,et al.  Membrane nanotubes: Novel communication between distant cells , 2013, Science China Life Sciences.

[19]  S. Rafii,et al.  Preferential transfer of mitochondria from endothelial to cancer cells through tunneling nanotubes modulates chemoresistance , 2013, Journal of Translational Medicine.

[20]  R. Pepperkok,et al.  Cell-to-cell communication: current views and future perspectives , 2013, Cell and Tissue Research.

[21]  X. Su,et al.  Tunneling-nanotube direction determination in neurons and astrocytes , 2012, Cell Death and Disease.

[22]  Hans-Hermann Gerdes,et al.  Developing Neurons Form Transient Nanotubes Facilitating Electrical Coupling and Calcium Signaling with Distant Astrocytes , 2012, PloS one.

[23]  K. Manova-Todorova,et al.  Tunneling Nanotubes , 2012, Communicative & integrative biology.

[24]  H. Haller,et al.  Vascular smooth muscle cells initiate proliferation of mesenchymal stem cells by mitochondrial transfer via tunneling nanotubes. , 2012, Stem cells and development.

[25]  H. Gerdes,et al.  Multi-Level Communication of Human Retinal Pigment Epithelial Cells via Tunneling Nanotubes , 2012, PloS one.

[26]  L. Marzo,et al.  Multifaceted Roles of Tunneling Nanotubes in Intercellular Communication , 2012, Front. Physio..

[27]  P. Lesault,et al.  Human Mesenchymal Stem Cells Reprogram Adult Cardiomyocytes Toward a Progenitor‐Like State Through Partial Cell Fusion and Mitochondria Transfer , 2011, Stem cells.

[28]  H. Westerblad,et al.  Myogenic skeletal muscle satellite cells communicate by tunnelling nanotubes , 2010, Journal of cellular physiology.

[29]  H. Gerdes,et al.  Intercellular transfer mediated by tunneling nanotubes. , 2008, Current opinion in cell biology.

[30]  Paul G. McMenamin,et al.  Cutting Edge: Membrane Nanotubes In Vivo: A Feature of MHC Class II+ Cells in the Mouse Cornea1 , 2008, The Journal of Immunology.

[31]  H. Gerdes,et al.  Tunneling nanotubes: A new route for the exchange of components between animal cells , 2007, FEBS letters.

[32]  J. Féher,et al.  Mitochondrial alterations of retinal pigment epithelium in age-related macular degeneration , 2006, Neurobiology of Aging.

[33]  N. Solenski,et al.  Nitric oxide impairs mitochondrial movement in cortical neurons during hypoxia , 2006, Journal of neurochemistry.

[34]  P. K. Kennady,et al.  Variation of mitochondrial size during the cell cycle: A multiparameter flow cytometric and microscopic study , 2004, Cytometry. Part A : the journal of the International Society for Analytical Cytology.

[35]  D. Davis,et al.  Cutting Edge: Membrane Nanotubes Connect Immune Cells12 , 2004, The Journal of Immunology.

[36]  Hans-Hermann Gerdes,et al.  Nanotubular Highways for Intercellular Organelle Transport , 2004, Science.

[37]  Laurence Zitvogel,et al.  Exosomes: composition, biogenesis and function , 2002, Nature Reviews Immunology.

[38]  N. Gregson,et al.  A COMPARATIVE STUDY OF BRAIN AND LIVER MITOCHONDRIA FROM NEW‐BORN AND ADULT RATS , 1969, Journal of neurochemistry.

[39]  De Angelis Francesca,et al.  Imaging of exosomes by broadband scanning microwave microscopy , 2016 .

[40]  S. Tooze,et al.  Correlative light and electron microscopy. , 2009, Methods in enzymology.