Research

Alexandra Brahmer

Physical exercise leads to systemic adaptations which promote long-term physical and mental health. The molecular basis underlying these bodily adaptations remains elusive. Extracellular vesicles (EVs) increase in the circulation upon diverse exercise interventions and are speculated to be involved in the physiological adaptation processes induced by regular physical exercise. In collaboration with the Department of Sports Medicine, Rehabilitation and Disease Prevention (University of Mainz) we study the release kinetics, cellular origin, cargo and functions of EVs that are released into the bloodstream in response to physical exercise – ExerVs.  

Our recent work revealed that cycling, as well as running exercise rapidly mobilizes ExerVs into the circulation starting in an early phase of exercise before exertion is reflected by increasing lactate levels, indicating that ExerV release may represent an active signalling mechanism. Detailed phenotyping of ExerVs via multiplexed-marker analysis methods (‘EV Array’ and ‘MACSPlex’) revealed that ExerVs originate from leukocytes, including lymphocytes (CD4+EVs, CD8+EVs), monocytes (CD14+EVs) and antigen-presenting cells (MHCI+EVs, MHCII+EVs), as well as endothelial cells (CD105+EVs, CD146+EVs) and platelets (CD41b+EVs, CD62P+EVs). 

Since EVs may carry DNA and circulating cell-free DNA (cfDNA) levels in blood also rise during exercise, we are investigating the topological association of cfDNA with ExerVs. Only a minor part of exercise-derived cfDNA is possibly transported via EVs. However, the molecular mechanisms of an active liberation of cfDNA as well as possible functions of cfDNA are not fully understood. Further characterization of the association of cfDNA with distinct ExerV subpopulations will determine the role of ExerVs in these processes.

Relevant Publications

Considerations for the Analysis of Small Extracellular Vesicles in Physical Exercise. Brahmer A, Neuberger EWI, Simon P and Krämer-Albers E-M (2020) Front. Physiol. 11:576150 DOI:10.3389/fphys.2020.576150

“Brainstorming”: Extracellular Vesicles in Physical Activity and Neuronal Health. Brahmer, A and Krämer-Albers, EM. Trillium Extracellular Vesicles, 2020, Vol. 2, 11-15

Platelets, endothelial cells and leukocytes contribute to the exercise-triggered release of extracellular vesicles into the circulation. Brahmer A, Neuberger E, Esch-Heisser L, Haller N, Jorgensen MM, Baek R, Möbius W, Simon P, Krämer-Albers EM. J Extracell Vesicles. 2019 May 28;8(1):1615820. doi: 10.1080/20013078.2019.1615820. eCollection 2019. PMID: 31191831 Free PMC article.

Association of Circulating Cell-free DNA Released During Physical Exercise with Extracellular Vesicles. Neuberger E, Brahmer A, Boztepe B, Krämer-Albers EM, Simon P. (2019)  American College of Sports Medicine (ACSM) Annual Meeting. Orlando, Florida, USA, 2019.

Physical exercise induces rapid release of small extracellular vesicles into the circulation. Frühbeis C, Helmig S, Tug S, Simon P, Krämer-Albers EM. J Extracell Vesicles. 2015 Jul 2;4:28239. doi: 10.3402/jev.v4.28239. eCollection 2015. PMID: 26142461 Free PMC article.

Release of bulk cell free DNA during physical exercise occurs independent of extracellular vesicles. Helmig S, Frühbeis C, Krämer-Albers EM, Simon P, Tug S. Eur J Appl Physiol. 2015 Nov;115(11):2271-80. doi: 10.1007/s00421-015-3207-8. Epub 2015 Jul 1. PMID: 26126838

Funding

Intramural Funding JGU Stufe 1

Collaborators

Perikles Simon

Elmo Neuberger

Susanne Helmig (Dep. Sportsmedicine, JGU Mainz)

Former Lab Members

Carsten Frühbeis

Katharina Mayr

Andrea Schnatz

The capacity to regenerate following axonal injury greatly varies amongst the different neuronal subtypes. While central neurons are generally assumed to be incapable of spontaneous regeneration, neurons of the peripheral nervous system encounter a growth-permissive milieu. Simultaneously, several studies have demonstrated de novo protein synthesis in injured peripheral axons locally providing the components necessary for an immediate regenerative response. Whereas the required mRNAs were shown to originate from the neuron's soma, the source of axonal ribosomes remained obscure.

We generated the so called “RiboTracker” mouse line expressing ribosomal protein L4 tagged with tdTomato (L4-tdTomato) in distinct cell types when crossed to specific Cre mice. We found that ribosomes are predominantly transferred from Schwann cells to peripheral axons following injury in vivo. In coculture-approaches using RiboTracker glial cells and wild type PNS or CNS tissues, we were also able to demonstrate a glia-to-axon transfer of L4-tdTomato⁺ ribosomes. Moreover, our observations strongly suggest vesicle-mediated transfer mechanisms of glial ribosomes injured axons (Müller*, Schnatz*, et al., 2018, Glia).

Relevant Publications

A predominantly glial origin of axonal ribosomes after nerve injury. Müller K*, Schnatz A*, Schillner M, Woertge S, Müller C, von Graevenitz I, Waisman A, van Minnen J, Vogelaar CF.Glia. 2018 Aug;66(8):1591-1610. doi: 10.1002/glia.23327. Epub 2018 Mar 25.PMID: 29575063

Collaborators

Tineke Vogelaar

Martin Auber, Christina Müller

EVs deliver RNAs, which have been implicated in phenotypic modulation of target cells. We are investigating the role of small RNAs associated with oligodendroglial EVs in neural plasticity and modulation of the oligodendroglial microenvironment. However, the topological and functional integration of RNAs as EV-cargo is more and more under debate in the field. Based on a rigorous RNA-Seq strategy, designed to exclude exogenous confounders, we are profiling small RNAs present in oligodendroglial EVs. Our aim is to identify RNA-binding proteins responsible for RNA sorting to EVs during EV-biogenesis and the mechanisms of RNA recovery in target cells.

Relevant Publications

Serum-free media supplements carry miRNAs that co-purify with extracellular vesicles. Auber M, Fröhlich D, Drechsel O, Karaulanov E, Krämer-Albers EM.  J Extracell Vesicles. 2019 Sep 9;8(1):1656042. doi: 10.1080/20013078.2019.1656042. PMID: 31552133; PMCID: PMC6746277.

Multifaceted effects of oligodendroglial exosomes on neurons: impact on neuronal firing rate, signal transduction and gene regulation. Fröhlich D, Kuo WP, Frühbeis C, Sun JJ, Zehendner CM, Luhmann HJ, Pinto S, Toedling J, Trotter J, Krämer-Albers EM. Philos Trans R Soc Lond B Biol Sci. 2014 Sep 26;369(1652):20130510. doi: 10.1098/rstb.2013.0510. PMID: 25135971 Free PMC article.

Oligodendroglial Argonaute protein Ago2 associates with molecules of the Mbp mRNA localization machinery and is a downstream target of Fyn kinase. Müller C, Schäfer I, Luhmann HJ, White R.  Front Cell Neurosci. 2015 Aug 25;9:328. doi: 10.3389/fncel.2015.00328. PMID: 26379499; PMCID: PMC4548153.

SncRNA715 Inhibits Schwann Cell Myelin Basic Protein Synthesis. Müller C, Hochhaus NM, Fontana X, Luhmann HJ, White R.  PLoS One. 2015 Aug 28;10(8):e0136900. doi: 10.1371/journal.pone.0136900. PMID: 26317513; PMCID: PMC4552632.

Myelin basic protein synthesis is regulated by small non-coding RNA 715. Bauer NM, Moos C, van Horssen J, Witte M, van der Valk P, Altenhein B, Luhmann HJ, White R. EMBO Rep. 2012 Sep;13(9):827-34. doi: 10.1038/embor.2012.97. Epub 2012 Jun 29. PMID: 22744314; PMCID: PMC3432817.

Funding

Nachwuchsförderprogramm 2017 der Carl-Zeiss-Stiftung (to CM)

Collaborators

Michael Pfaffl

Dominik Buschmann

Benedikt Kirchner (TUM München)

Christian Preußer

Former Lab Members

Martin Auber

Dominik Fröhlich

Hannah Mende

Andrea Schnatz

To monitor the delivery of EVs to target cells in vivo, we make use of a reporter strategy.We utilize transgenic mouse models (reporters) to determine EV-mediated neural cell communication and its prevalence in distinct areas of the brain. The strategy involves oligodendroglial CreERT2 drivers crossed to Rosa26-loxP reporter mice. Transfer of CreERT2 to neurons results in neuronal reporter gene activation, which can be quantified in brain slices within different brain regions. We further confirm neuronal target cell recombination due to EV-transfer by genetically interfering with EV-biogenesis and release in these reporter mice.

Open position for Master student avaiable

Relevant publications

Neurotransmitter-triggered transfer of exosomes mediates oligodendrocyte-neuron communication. Frühbeis C, Fröhlich D, Kuo WP, Amphornrat J, Thilemann S, Saab AS, Kirchhoff F, Möbius W, Goebbels S, Nave KA, Schneider A, Simons M, Klugmann M, Trotter J, Krämer-Albers EM. PLoS Biol. 2013 Jul;11(7):e1001604. doi: 10.1371/journal.pbio.1001604. Epub 2013 Jul 9. PMID: 23874151 Free PMC article.

Funding

SPP Young Investigator Start-Up Fund (to Andrea Schnatz)

Collaborators

Frank Kirchhoff

Anja Scheller

Laura Stopper (Homburg Saar)

Remy Sadoul

Former Lab Members

Kerstin Barth

Katharina Mayr

Janina Kuschmann

Christina Müller

We perform proteomic and transcriptomic profiling of small extracellular vesicles and exosomes isolated from primary oligodendrocytes (OL-sEVs) to characterize their molecular content. Using different isolation procedures, we aim at deciphering different OL-sEV subtypes and correlating functions. Our previous work indicates that OL-sEVs promote the neuronal metabolic activity and axonal transport. We use transgenic mouse models, which exhibit secondary axonal degeneration (e.g. PLP-ko and CNP-ko mice) and study mutant-derived OL-sEVs, lacking the functional competence of wild-type OL-sEVs, to decipher the molecular cargo and signalling pathways relevant for neuronal support and axonal maintenance.

Relevant Publications

Oligodendrocytes Provide Antioxidant Defense Function for Neurons by Secreting Ferritin Heavy Chain. Mukherjee C, Kling T, Russo B, Miebach K, Kess E, Schifferer M, Pedro LD, Weikert U, Fard MK, Kannaiyan N, Rossner M, Aicher ML, Goebbels S, Nave KA, Krämer-Albers EM, Schneider A, Simons M. Cell Metab. 2020 Jun 5:S1550-4131(20)30300-4. doi: 10.1016/j.cmet.2020.05.019. Online ahead of print. PMID: 32531201

Multifaceted effects of oligodendroglial exosomes on neurons: impact on neuronal firing rate, signal transduction and gene regulation. Fröhlich D, Kuo WP, Frühbeis C, Sun JJ, Zehendner CM, Luhmann HJ, Pinto S, Toedling J, Trotter J, Krämer-Albers EM. Philos Trans R Soc Lond B Biol Sci. 2014 Sep 26;369(1652):20130510. doi: 10.1098/rstb.2013.0510. PMID: 25135971 Free PMC article.

Neurotransmitter-triggered transfer of exosomes mediates oligodendrocyte-neuron communication. Frühbeis C, Fröhlich D, Kuo WP, Amphornrat J, Thilemann S, Saab AS, Kirchhoff F, Möbius W, Goebbels S, Nave KA, Schneider A, Simons M, Klugmann M, Trotter J, Krämer-Albers EM. PLoS Biol. 2013 Jul;11(7):e1001604. doi: 10.1371/journal.pbio.1001604. Epub 2013 Jul 9. PMID: 23874151 Free PMC article.

Oligodendrocytes secrete exosomes containing major myelin and stress-protective proteins: Trophic support for axons? Krämer-Albers EM, Bretz N, Tenzer S, Winterstein C, Möbius W, Berger H, Nave KA, Schild H, Trotter J. Proteomics Clin Appl. 2007 Nov;1(11):1446-61. doi: 10.1002/prca.200700522. Epub 2007 Oct 16. PMID: 21136642

Funding

DFG KR3668/1-1 and KR3668/1-2

Collaborators

Klaus-Armin Nave

Wiebke Möbius

Hauke Werner (Göttingen)

Sandra Göbbels (Göttingen)

Mikael Simons

Leticia Peris

Stefan Tenzer

Former Lab Members

Jesa Amphornrat

Martin Auber

Kerstin Barth

Niko Bretz

Dominik Fröhlich

Carsten Frühbeis

Marla Herr

Wen Ping Kuo-Elsner

Sebastian Thilemann

Monika Tießen

Extracellular Vesicles in neuron-glia communication and CNS homeostasis

The nervous system is formed by a network of closely interacting neurons and glial cells. Our research interest is focussed on the molecular mechanisms of cell communication between neurons and glial cells, in particular myelinating oligodendrocytes and neurons, which form a functional unit in the CNS.

We are studying membrane-enclosed vesicles, termed Extracellular Vesicles, which deliver biomolecules including lipids, proteins and nucleic acids between cells. Our work revealed that myelinating oligodendrocytes release Extracellular Vesicles (largely exosomes derived from the endomembrane system of cells), which travel to neurons in response to neuronal activity and promote neuronal maintenance. We are investigating the functional role of glia-derived Extracellular Vesicles in long-term neuronal maintenance and homeostasis and their molecular mode of action using in vitro models as well as transgenic mouse models. We aim at better understanding of the homeostatic as well as neurodegenerative processes, which occur in brain disorders such as Multiple Sclerosis and moreover during aging.

Furthermore, Extracellular Vesicles provide a means to deliver physiological signals and cargo also across the borders of the brain and we would like to better understand their role in brain-periphery communication. To this end, we are studying human and mouse models of exercise known to promote brain homeostasis and prevent neurodegeneration.

References and review articles:

Mechanisms of axonal support by oligodendrocyte-derived extracellular vesicles. Krämer-Albers EM., Werner HB. Nat Rev Neurosci. 2023 May 31. doi: 10.1038/s41583-023-00711-y.

Oligodendrocytes support axonal transport and maintenance via exosome secretion. Frühbeis C, Kuo-Elsner WP, Müller C, Barth K, Peris L, Tenzer S, Möbius W, Werner HB, Nave KA, Fröhlich D, Krämer-Albers EM. PLoS Biol. 2020 Dec 22;18(12):e3000621. doi: 10.1371/journal.pbio.3000621.

Neurotransmitter-triggered transfer of exosomes mediates oligodendrocyte-neuron communication. Frühbeis C, Fröhlich D, Kuo WP, Amphornrat J, Thilemann S, Saab AS, Kirchhoff F, Möbius W, Goebbels S, Nave KA, Schneider A, Simons M, Klugmann M, Trotter J, Krämer-Albers EM. PLoS Biol. 2013 Jul;11(7):e1001604. doi: 10.1371/journal.pbio.1001604.