Subcellular localization of sphingosine 1-phosphate receptors in synapses of the mouse cortex

Summary, in English

Sphingosine 1-phosphate (S1P) has pleiotropic biological functions in the regulation of proliferation, survival, migration, inflammation or angiogenesis. S1P acts as intracellular second messenger,
as well as extracellular receptor ligand via five G-protein coupled
receptors (S1PR1-5). In the brain, S1P regulates neuronal proliferation or apoptosis, excitatory neurotransmission and neuroglia
activation, and S1P metabolism alterations have been associated to
neurodegenerative disorders. Interestingly, an agonist targeting
S1PR1,3,4,5 (FTY720) shows neuroprotective properties through
mechanisms that are not fully unveiled, but might include the
control of neuroinflammation, vascular deterioration and synaptic
dysfunction. The subcellular distribution of S1PRs in nerve
terminals is hitherto unknown. The present study aimed at
determining the synaptic localisation of S1PRs in the cortex of
adult male mice. Synaptosomes were purified from mouse cortex
homogenates using a sucrose density gradient centrifugation, and
further fractioned into pre-, post- and extrasynaptic zones using a
series of pH shifts that allow successive solubilisation of synaptic
components (Phillips et al., Neuron 32:63, 2001). Western blot
analysis of the obtained fractions, as well as total protein extracts
from cortex revealed that S1PR1 is present in similar amounts in
total extracts, synaptosomes and the extrasynaptic fraction, but
absent from the pre- and postsynaptic fractions. S1PR2 was
ubiquitously distributed, showing 3-fold higher levels in the
presynaptic zone than the post- (P<0.05) and extrasynaptic
(P<0.05) fractions. Similarly, S1PR4 was also distributed across
all synaptic fractions but 4-fold more enriched presynaptically.
S1PR3 and S1PR5 were not efficiently detected by immunoblotting
in synaptosomes and synaptic fractions. Altogether, these results
point towards S1PR2 and S1PR4 being particularly well poised to
directly modulate synaptic transmission and plasticity upon S1P
activation.