EP 12. Fingolimod promotes nerve regeneration by modulating Lysophospholipid signaling

The lysophospholipids sphingosine-1-phosphate (S1P) and lysophosphatidic acid (LPA) are pleiotropic signaling molecules with a broad range of physiological functions. Targeting the S1P 1 receptor on lymphocytes with the immunomodulatory drug fingolimod has proven effective in the treatment of multiple sclerosis. An emerging body of experimental evidence points to additional direct effects on cells of the central and peripheral nervous system. Furthermore, fingolimod has been reported to reduce LPA synthesis via inhibition of the lysophospholipase autotaxin. Here we investigated whether modulation of particular signaling aspects of S1P as well as LPA by fingolimod might propagate peripheral nerve regeneration in vivo and independent of its anti-inflammatory potency. To distinguish potential direct nerve specific effects from the established immunosuppressive action of fingolimod, we performed sciatic nerve crush in wildtype C57BL/6 as well as in immunodeficient Rag 1 - / - and Foxn 1 - / - mice. Analyses were based on walking track analysis and electrophysiology, histology, cAMP formation as well as oxidative stress assessment by dinitrophenyl-labeling of free protein carbonyls. Quantification of different LPA species was performed by liquid chromatography coupled to tandem mass spectrometry. Furthermore, functional consequences of LPA level reduction by the autotaxin inhibitor PF-8380 were investigated. Clinical, electrophysiological and histological measures indicated an improvement of nerve regeneration under fingolimod treatment that is partly independent of its anti-inflammatory properties. Fingolimod induced an elevation of axonal cAMP, a crucial factor for axonal outgrowth. Consistently, immunohistochemistry indicated S1P 1 receptor internalization in cells of the sciatic nerve. Additionally, fingolimod attenuated oxidative tissue damage and significantly reduced LPA levels in the injured nerve. PF-8380 induced reduction of LPA levels correlated with improved myelin thickness. Collectively, our work demonstrates that modulation of lysophospholipid signaling in the peripheral nervous system by fingolimod may enhance nerve regeneration by acting on multiple molecular and cellular levels and partly independent of its anti-inflammatory effects. In addition to the established role of fingolimod as a modulator of S1P receptor mediated signaling, the inhibition of LPA synthesis may represent a yet unrecognized mechanism that contributes to the presumptive remyelinating effect of fingolimod.