Redefining the Role of
Metallothionein within the Injured Brain
EXTRACELLULAR METALLOTHIONEINS PLAY AN IMPORTANT ROLE IN THE ASTROCYTE-NEURON
RESPONSE TO INJURY.
Roger S. Chung1, Milena Penkowa2, Justin Dittmann1,
Carolyn E. King3,
Carole Bartlett3,
Johanne W. Asmussen2, Juan Hidalgo4,
Javier Carrasco4,
Yee Kee J. Leung1, Adam K. Walker1, Samantha J. Fung1,
Sarah A. Dunlop3,
Melinda Fitzgerald3,
Lyn D. Beazley3,
Meng I. Chuah1, James C. Vickers1, and Adrian K. West1
1NeuroRepair Group, Menzies Research Institute, University of
Tasmania, Private Bag 58, Hobart, Tasmania 7001, Australia,
2Section
of Neuroprotection, Faculty of Health Sciences, University of Copenhagen,
Copenhagen DK2200, Denmark,
3School
of Animal Biology, University of Western Australia, Nedlands, Western Australia
6907, Australia, and
4Institute
of Neurosciences and Department of Cellular Biology, Physiology and Immunology,
Animal Physiology Unit, Faculty of Sciences, Autonomous University of Barcelona,
Bellaterra, Barcelona 08193, Spain
Journal of Biological Chemistry, Vol. 283, Issue 22, 15349-15358, May 30,
2008.
Abstract: A number of intracellular
proteins that are protective after brain injury are classically thought to exert
their effect within the expressing cell. The astrocytic metallothioneins (MT)
are one example and are thought to act via intracellular free radical scavenging
and heavy metal regulation, and in particular zinc. Indeed, we have previously
established that astrocytic MTs are required for successful brain healing. Here
we provide evidence for a fundamentally different mode of action relying upon
intercellular transfer from astrocytes to neurons, which in turn leads to
uptake-dependent axonal regeneration. First, we show that MT can be detected
within the extracellular fluid of the injured brain, and that cultured
astrocytes are capable of actively secreting MT in a regulatable manner. Second,
we identify a receptor, megalin, that mediates MT transport into neurons. Third,
we directly demonstrate for the first time the transfer of MT from astrocytes to
neurons over a specific time course in vitro. Finally, we show that MT is
rapidly internalized via the cell bodies of retinal ganglion cells in vivo and
is a powerful promoter of axonal regeneration through the inhibitory environment
of the completely severed mature optic nerve. Our work suggests that the
protective functions of MT in the central nervous system should be widened from
a purely astrocytic focus to include extracellular and intra-neuronal roles.
This unsuspected action of MT represents a novel paradigm of astrocyte-neuronal
interaction after injury and may have implications for the development of
MT-based therapeutic agents.
New insight into the
molecular pathways of metallothionein-mediated neuroprotection and regeneration
R. S. Chung*, J. Hidalgo† and A. K. West*
*NeuroRepair
Group, Menzies Research Institute, University of Tasmania, Hobart, Tasmania,
Australia
†Institute of Neurosciences and Department of
Cellular Biology, Physiology and Immunology, Animal Physiology Unit, Faculty
of Sciences, Autonomous University of Barcelona, Bellaterra, Barcelona, Spain
Address correspondence and reprint requests to
R. S. Chung, NeuroRepair Group, Menzies Research Institute, University of
Tasmania, Private Bag 58, Hobart, Tasmania Australia 7001.
E-mail:
rschung@utas.edu.au
Keywords: MAG, myelin-associated glycoprotein;
MT, metallothionein; LDL, low density lipoprotein; CREB, cAMP response element
binding protein.
There is a large body of
evidence demonstrating that metallothioneins (MTs) expressed in astrocytes
following CNS injury, exhibit both neuroprotective and neuroregenerative
properties and are critical for recovery outcomes. As these proteins lack
signal peptides, and have well characterized free radical scavenging and heavy
metal binding properties, the neuroprotective functions of MTs have been
attributed to these intracellular roles. However, there is an increasing
realization that the neuroprotective functions of MTs may also involve an
extracellular component. In this issue of Journal of Neurochemistry,
Ambjørn et al. reveal considerable insight into this novel function of
MTs. In this review, we examine the seminal work of Ambjørn et al. in
the context of our current understanding of the role of MT in astrocyte-neuron
interactions in the injured brain, and also discuss the significant
therapeutic potential of their work.
Full article here
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Metallothionein and a peptide modeled after
metallothionein, EmtinB, induce neuronal differentiation and survival through
binding to receptors of the low-density lipoprotein receptor family.
Malene Ambjørn*, Johanne W. Asmussen*,†, Mats
Lindstam*, Kamil Gotfryd*, Christian Jacobsen‡, Vladislav V. Kiselyov*, Søren K.
Moestrup‡, Milena Penkowa†, Elisabeth Bock* and Vladimir Berezin*
*Protein Laboratory, Institute of Neuroscience
and Pharmacology, University of Copenhagen, Copenhagen, Denmark
†Section of Neuroprotection, Institute of Neuroscience and Pharmacology,
University of Copenhagen, Copenhagen, Denmark
‡Institute of Medical Biochemistry, University of Aarhus, Aarhus, Denmark
Address correspondence and reprint requests to Vladimir Berezin, Protein
Laboratory, Institute of Neuroscience and Pharmacology, University of
Copenhagen, Panum Institute Building 6.2, Blegdamsvej 3, DK-2200 Copenhagen N,
Denmark. E-mail: berezin@plab.ku.dk
Keywords: 7DIV, 7 days in vitro; Bcl-2, B-cell leukemia/lymphoma-2; BH,
Bcl-2 homology; BimS, Bcl-2 interacting member of cell death, short isoform; BSA,
bovine serum albumin; CGN, cerebellar granule neuron; CREB, cAMP response
element binding protein; ERK, extracellular signal-regulated kinase; LDLR,
low-density lipoprotein receptor; LRP, low-density lipoprotein receptor-related
protein; MT, metallothionein; NB-A, neurobasal-A; PACE, phosphospecific antibody
cell-based ELISA; PBS, phosphate-buffered saline; PKB/Akt, protein kinase B;
RAP, receptor-associated protein-1.
Abstract
Accumulating evidence suggests that metallothionein (MT)-I and -II promote
neuronal survival and regeneration in vivo. The present study investigated the
molecular mechanisms underlying the differentiation and survival-promoting
effects of MT and a peptide modeled after MT, EmtinB. Both MT and EmtinB
directly stimulated neurite outgrowth and promoted survival in vitro using
primary cultures of cerebellar granule neurons. In addition, expression and
surface localization of megalin, a known MT receptor, and the related
lipoprotein receptor-related protein-1 (LRP) are demonstrated in cerebellar
granule neurons. By means of surface plasmon resonance MT and EmtinB were found
to bind to both megalin and LRP. The bindings were abrogated in the presence of
receptor-associated protein-1, an antagonist of the low-density lipoprotein
receptor family, which also inhibited MT- and EmtinB-induced neurite outgrowth
and survival. MT-mediated neurite outgrowth was furthermore inhibited by an
anti-megalin serum. EmtinB-mediated inhibition of apoptosis occurred without a
reduction of caspase-3 activity, but was associated with reduced expression of
the pro-apoptotic B-cell leukemia/lymphoma-2 interacting member of cell death (BimS).
Finally, evidence is provided that MT and EmtinB activate extracellular
signal-regulated kinase, protein kinase B, and cAMP response element binding
protein. Altogether, these results strongly suggest that MT and EmtinB induce
their neuronal effects through direct binding to surface receptors belonging to
the low-density lipoprotein receptor family, such as megalin and LRP, thereby
activating signal transduction pathways resulting in neurite outgrowth and
survival.
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