Selective Deletion of S1P5 Receptors Reduces Remyelination in the Curprizone Model

Background:

Multiple Sclerosis (MS) is a multi-faceted inflammatory CNS disease characterized by oligodendrocyte damage and death resulting in a progressive loss of myelin and axons. The mechanisms responsible for myelin loss are complex and therapies that promote oligodendrocyte survival, differentiation and remyelination may drive neuroprotection. Activation of Sphingosine-1-phosphate 5 receptors (S1P₅), which are predominately expressed in oligodendrocytes, has been shown to promote oligodendrocyte survival and differentiation in vitro (Jaillard et al., 2005). However, the role of S1P₅ receptors in regulating demyelination and remyelination in vivo is still unknown.   

Objectives: Here we examine demyelination and remyelination in S1P₅knockout mice following exposure to cuprizone.  

Methods: Selective S1P₅ receptor knockout (KO) mice were generated in collaboration with  Regeneron and bred in our animal facility. No obvious myelin or other defects are detectable in KO animals without challenge. S1P₅ KO mice and wild type (WT) litter mate controls received 4 wks of unrestricted access to rodent chow containing 0.2% cuprizone.  Mice were euthanized following exposure to cuprizone and the level of demyelination in the corpus callosum (CC) analyzed. Spontaneous remyelination will occur in cuprizone fed animals once the cuprizone diet is removed and animals receive access to normal chow. To examine remyelination rate in mice lacking the S1P₅receptor, cohorts of both WT and KO mice were euthanized 7, 14, and 21 days following access to normal chow (after 4 wks of cuprizone).

Results:

4 wks of cuprizone diet produced significant demyelination in the CC of both WT and S1P₅ KO mice as measured by Luxol Fast Blue (LFB) staining (21% & 13% respectively, p < .05 as compared to mice on control diet). WT mice exposed to 4 weeks of cuprizone diet followed by different periods of normal chow demonstrated gradual remyelination over the course of 21 days (43% at 7 days & 66% at 21 days). S1P₅KO mice also demonstrated some remyelination by day 21, however the level of remyelination was significantly reduced as compared to WT controls (45% at 21 days in KO vs 66% in WT controls, p < .05). Similar results occur following IHC staining with myelin oligodendrocyte glycoprotein (MOG).

Conclusions:

The above results demonstrate a clear role of the S1P₅ receptor in regulating remyelination in vivo.  Animals with selective deletion of the S1P₅ receptor display a significant delay in the rate of remyelination. Although additional studies are warranted, these results suggest that the S1P₅ receptor might be a good target to drive remyelination in demyelinating diseases.