Abstract
Background: Fingolimod (FTY720) is the first sphingosine-1-phosphate
(S1P) receptor modulator approved for the treatment of multiple
sclerosis. The phosphorylated active metabolite FTY720-phosphate (FTY-P)
interferes with lymphocyte trafficking. In addition, it accumulates in
the CNS and reduces brain atrophy in multiple sclerosis (MS), and
neuroprotective effects are hypothesized.
Methods: Human primary astrocytes as well as human astrocytoma cells
were stimulated with FTY-P or S1P. We analyzed gene expression by a
genome-wide microarray and validated induced candidate genes by
quantitative PCR (qPCR) and ELISA. To identify the S1P-receptor subtypes
involved, we applied a membrane-impermeable S1P analog (dihydro-S1P),
receptor subtype specific agonists and antagonists, as well as RNAi
silencing.
Results: FTY-P induced leukemia inhibitory factor (LIF), interleukin 11
(IL11), and heparin-binding EGF-like growth factor (HBEGF) mRNA, as well
as secretion of LIF and IL11 protein. In order to mimic an inflammatory
milieu as observed in active MS lesions, we combined FTY-P application
with tumor necrosis factor (TNF). In the presence of this key
inflammatory cytokine, FTY-P synergistically induced LIF, HBEGF, and
IL11 mRNA, as well as secretion of LIF and IL11 protein. TNF itself
induced inflammatory, B-cell promoting, and antiviral factors (CXCL10,
BAFF, MX1, and OAS2). Their induction was blocked by FTY-P. After
continuous exposure of cells to FTY-P or S1P for up to 7 days, the
extent of induction of neurotrophic factors and the suppression of
TNF-induced inflammatory genes declined but was still detectable. The
induction of neurotrophic factors was mediated via surface S1P receptors
1 (S1PR1) and 3 (S1PR3).
Conclusions: We identified effects of FTY-P on astrocytes, namely
induction of neurotrophic mediators (LIF, HBEGF, and IL11) and
inhibition of TNF-induced inflammatory genes (CXCL10, BAFF, MX1, and
OAS2). This supports the view that a part of the effects of fingolimod
may be mediated via astrocytes.
