Sphingosine 1‐phosphate but not Fingolimod protects neurons against excitotoxic cell death by inducing neurotrophic gene expression in astrocytes

Abstract

Abbreviations used: AD, Alzheimer's disease; BBB, blood-brain barrier; BDNF, brain-derived neurotrophic factor; DMEM, Dulbecco's modified Eagle's medium; DMSO, dimethyl sulfoxide; ERK, extracellular signal regulated kinase; FBS, fetal bovine serum; FTY720-P, FTY720-phosphate; HBEGF, heparin-binding epidermal growth factor-like growth factor; LIF, leukemia inhibitory factor; NMDA, N-methyl-d-aspartate; PDGFB, platelet-derived growth factor; PI, propidium iodide; RRID, research resource identifier; S1P, sphingosine 1-phosphate; S1PR1, sphingosine 1-phosphate receptor 1; S1PR2, sphingosine 1-phosphate receptor 2; S1PR3, sphingosine 1-phosphate receptor 3; SphK1/2, sphingosine kinase 1; SphK2, sphingosine kinase 2. AbstractSphingosine 1-phosphate (S1P) is an essential lipid metabolite that signals through a family of five G protein-coupled receptors, S1PR1-S1PR5, to regulate cell physiology.The multiple sclerosis drug Fingolimod (FTY720) is a potent S1P receptor agonist that causes peripheral lymphopenia. Recent research has demonstrated direct neuroprotective properties of FTY720 in several neurodegenerative paradigms; however, neuroprotective properties of the native ligand S1P have not been established.We aimed to establish the significance of neurotrophic factor up-regulation by S1P for neuroprotection, comparing S1P with FTY720. S1P induced brain-derived neurotrophic factor (BDNF), leukemia inhibitory factor (LIF), platelet-derived growth factor B (PDGFB), and heparin-binding EGF-like growth factor (HBEGF) gene expression in primary human and murine astrocytes, but not in neurons, and to a much greater extent than FTY720. Accordingly, S1P but not FTY720 protected cultured neurons against excitotoxic cell death in a primary murine neuron-glia coculture model, and a neutralizing antibody to LIF blocked this S1P-mediated neuroprotection. Antagonists of S1PR1 and S1PR2 both inhibited S1P-mediated neurotrophic gene induction in human astrocytes, indicating that simultaneous activation of both receptors is required. S1PR2 signaling was transduced through Gα 13 and the small GTPase Rho, and was necessary for the up-regulation and activation of the transcription factors FOS and JUN, which regulate LIF, BDNF, and HBEGF transcription. In summary, we show that S1P protects hippocampal neurons against excitotoxic cell death through up-regulation of neurotrophic gene expression, particularly LIF, in astrocytes. This up-regulation requires both S1PR1 and S1PR2 signaling. FTY720 does not activate S1PR2, explaining its relative inefficacy compared to S1P.

Protective Functions of Reactive Astrocytes Following Central Nervous System Insult

“…Mature HB-EGF signals through EGFR, ErbB4 and a newly defined N-arginine dibasic convertase, but may also be able to induce ErbB2 through heterodimerization ( 214 , 225 – 227 ). In astrocytes, upregulation of HBEGF mRNA has been observed in response to sphingosine-1-phosphat (S1P)-receptor activation by S1P or S1P receptor modulator fingolimod ( 92 , 93 ). This may be dependent on combined S1P1R and S1P2R signaling and the activation of the immediate early transcription factors ERG1 and AP1, indicating that astrocyte-derived HB-EGF is part of a rapid response mechanism that counteracts pro-inflammatory astrocyte functions ( 93 ).…”

“…In astrocytes, upregulation of HBEGF mRNA has been observed in response to sphingosine-1-phosphat (S1P)-receptor activation by S1P or S1P receptor modulator fingolimod ( 92 , 93 ). This may be dependent on combined S1P1R and S1P2R signaling and the activation of the immediate early transcription factors ERG1 and AP1, indicating that astrocyte-derived HB-EGF is part of a rapid response mechanism that counteracts pro-inflammatory astrocyte functions ( 93 ). Indeed, it has been suggested that HB-EGF suppresses the nuclear translocation of NF-κB by inhibition of IκB kinase (IKK) mediated inhibitor of κB (IκB) degradation ( 222 ).…”

“…Consequently, astrocyte-derived LIF may potentiate stem cell renewal in the adult SVZ and increase the regenerative capacities following CNS insult ( 101 , 262 ) ( Figure 2 ) . Although it is not entirely clear what mechanisms modulate the upregulation of Lif expression in astrocytes, S1PR signaling has been shown to be a potent inducer ( 92 , 93 ). Apart from its beneficial functions on stem cell regeneration and neurogenesis, accumulating evidence shows that LIF plays essential roles during oligodendrocyte maturation and function in the context of autoimmune inflammation and remyelination ( 102 – 107 ).…”

Sphingosine-1-Phosphate: Its Pharmacological Regulation and the Treatment of Multiple Sclerosis: A Review Article

“…Sphingosine-1-P, by stimulating both S1PR-1 and S1PR-2, may induce gene expression encoding for the production of protective astrocyte neurotrophic factors, not achieved by S1PR-1 modulation alone [ 58 ]. Bi-receptor S1PR-1 and S1PR-2 stimulation [ 59 ] appears to be necessary to up-regulate neurotrophic mRNA expression, which only takes place in astrocytes [ 60 , 61 ]. To date there are no pharmacological agents of which we are aware that operate jointly or exclusively at both S1PR-1 and S1PR-2 under investigation as potential medications for MS, yet the importance of regulating astrocyte proliferation and astrogliosis would be reasons enough to examine agents that can synergistically modulate both receptor subsets.…”

The ceramide-S1P pathway as a druggable target to alleviate peripheral neuropathic pain

“…signaling via G 13 and the small G-protein RhoA that upregulates and activates the transcription factors Fos and Jun, which regulate the transcription of LIF [122].…”