EURON and THEME joint PhD meeting

45
EURON and THEME joint meeting 2011
Characterization of Kir channel expression in
Schwann cells of the sciatic nerve in a mouse model of
metachromatic leukodystrophy
Cin-He Chang 1 , Lihua Wang-Eckhardt 2 , Matthias Eckhardt 2 , Gerald Seifert 1 ,
Volkmar Gieselmann 2 , Christian Steinhäuser 1
1 2 Institute of Cellular Neurosciences and Institute of Biochemistry and Molecular Biology, Medical Faculty,
University of Bonn, Germany
Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder caused by
deficiency of arylsulfatase A (ASA) and sulfatide storage. ASA deficient mice are
an animal model for MLD, which, however, show a relatively mild phenotype. An
improved mouse model of MLD, showing increased sulfatide synthesis, has been
generated that displays increased sulfatide storage in neural cells of the brain
and peripheral nervous system. In the peripheral nerves of these mice, hypo- and
demyelination was observed, leading to a slowed propagation of action potentials
(Ramakrishnan et al., 2007). Analysis of transcript and protein expression revealed
an upregulation of the inward rectifying K + channel subunit Kir4.1 which in the
nervous system is expressed solely by glial cells. To investigate whether these
changes are accompanied by alterations in Kir4.1 channel function, we applied
the patch clamp-technique to Schwann cells freshly isolated from sciatic nerves
of ASA-/- mice, ASA-/- mice overexpressing the sulfatide synthesizing cerebroside
sulfotransferase in Schwann cells (TG/ASA-/-), and wildtype littermates (WT)
(postnatal day 300 – 500).
Schwann cells from WT and ASA-deficient mice displayed depolarized membrane
potentials of about -45 mV and a high input resistance (about 400 ΜΩ). These
findings did not imply significant expression of functional Kir channels. In line with
this assumption, neither WT nor ASA-deficient mice displayed Ba2+ (100 µM)sensitive
inward currents at negative membrane potentials. In conclusion, data
obtained so far suggest that in these MLD models, upregulation of Kir4.1 mRNA
and protein in peripheral nerves is not accompanied by increased expression of
functional channels.
In the second part of my Ph.D. thesis I’m investigating the functional impact of
inducible astrocyte-specific ablation of GABA B receptors. Analyses in WT mice
revealed that the GABA B R1 subunit is expressed in almost all astrocytes of the
hippocampus, whereas pyramidal neurons of the same brain region express
both GABA B R1 and GABA B R2 subunits. Recent studies demonstrated that
GABA B receptor activation in astrocytes leads to increase in [Ca 2+ ]i, release of
gliotransmitters and modulation of synaptic signalling, although the underlying