FTY720 (fingolimod) efficacy in an animal model of multiple sclerosis requires astrocyte sphingosine 1-phosphate receptor 1 (S1P ₁ ) modulation

Abstract

Sphingosine 1-phosphate (S1P), a lysophospholipid, has gained relevance to multiple sclerosis through the discovery of FTY720 (fingolimod), recently approved as an oral treatment for relapsing forms of multiple sclerosis. Its mechanism of action is thought to be immunological through an active phosphorylated metabolite, FTY720-P, that resembles S1P and alters lymphocyte trafficking through receptor subtype S1P 1 . However, previously reported expression and in vitro studies of S1P receptors suggested that direct CNS effects of FTY720 might theoretically occur through receptor modulation on neurons and glia. To identify CNS cells functionally contributing to FTY720 activity, genetic approaches were combined with cellular and molecular analyses. These studies relied on the functional assessment, based on clinical score, of conditional null mouse mutants lacking S1P 1 in CNS cell lineages and challenged by experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. All conditional null mutants displayed WT lymphocyte trafficking that responded normally to FTY720. In marked contrast, EAE was attenuated and FTY720 efficacy was lost in CNS mutants lacking S1P 1 on GFAP-expressing astrocytes but not on neurons. In situ hybridization studies confirmed that astrocyte loss of S1P 1 was the key alteration in functionally affected mutants. Reductions in EAE clinical scores were paralleled by reductions in demyelination, axonal loss, and astrogliosis. Receptor rescue and pharmacological experiments supported the loss of S1P 1 on astrocytes through functional antagonism by FTY720-P as a primary FTY720 mechanism. These data identify nonimmunological CNS mechanisms of FTY720 efficacy and implicate S1P signaling pathways within the CNS as targets for multiple sclerosis therapies.ultiple sclerosis is an autoimmune disorder characterized by CNS demyelination, inflammation, and neurodegeneration (1). Current Food and Drug Administration (FDA)-approved therapies predominantly target immunological pathways through injectable agents. FTY720 (known clinically as fingolimod) is an oral drug that has shown efficacy in human multiple sclerosis clinical trials (2, 3), and in September 2010, received FDA approval as an oral therapy for relapsing forms of multiple sclerosis. The actions of FTY720 seem to involve at least two, paradoxically, opposite sphingosine 1-phosphate (S1P) receptor mechanisms operating in the immune system: agonism and functional antagonism. FTY720 is phosphorylated in vivo to produce the active metabolite FTY720-P, which is a nonselective S1P receptor agonist for four of the five known S1P receptors (4-6), and can function as an agonist in vivo (7). However, FTY720-P can also act as a functional antagonist, where bound S1P receptors are irreversibly internalized and degraded rather than recycled back to the cell surface as occurs with S1P ligands (8, 9); additionally, FTY720-P signaling may persist even after receptor internalization (10). The biological locus responsible for FTY720 efficac...

Sphingosine 1-Phosphate Receptor-1 Enhances Mitochondrial Function and Reduces Cisplatin-Induced Tubule Injury

“…In experimental autoimmune encephalomyelitis, a mouse model of multiple sclerosis, FTY720 may have a direct neuroprotective effect that is dependent on the S1pr1 expression in astrocytes. 34 In our studies, stimulation of PT-S1P1 reduced cisplatin-induced apoptosis, perhaps by blocking the mitochondrial apoptotic pathway, but additional studies are needed to further elucidate the mechanisms of PT-S1P1 stimulation.…”

The S1P1 receptor-selective agonist CYM-5442 reduces the severity of acute GVHD by inhibiting macrophage recruitment

“…Binding of S1P receptor agonists, including FTY720 and CYM, to S1P receptors causes internalization and may cause functional antagonism, persistent signaling or both. 12,50,51 The ways in which internalization, degradation, and sustained signaling collectively regulate S1P receptor function are not yet understood. Further studies are needed to fully elucidate the molecular mechanism by which the S1P agonists act.…”

“…10,11 The binding of FTY720 to S1P 1,3,4,5 induces receptor internalization and results in functional antagonism. 9,12,13 FTY720 has been shown to be a promising immunosuppressive agent for the treatment of autoimmune disease, promotion of solid organ engraftment and inhibition of aGVHD. 8,[14][15][16][17][18][19][20][21] However, the mechanism underlying the action of FTY720 is not completely known.…”

Astrocytes in the tempest of multiple sclerosis

“…Through reduction of S1P1 signaling in lymphocytes, FTY720 slows egress kinetics of pro-inflammatory Th17 cells from lymph nodes, decreasing infiltration of the CNS and consequent neuroinflammation. Still, beneficial effect of fingolimod in neuroinflammation seems to be also dependent on its direct influence on astrocytes [110,111]. Down-regulation of S1P1 signaling in astrocytes reduce reactive astrogliosis and improve gap-junctional communication among these cells, which might contribute to structural restoration of the CNS parenchyma in MS patients [110].…”