Lysophosphatidic Acid Guides The Homing Of Transplanted Olfactory Ensheathing Cells To The Lesion Site After Spinal Cord Injury In Rats

Spinal cord injury(SCI)often causes severe and irreversible central nervous system dysfunction.Olfactory ensheathing cells(OECs),a special type of glial cell,are responsible for the prominent renewal capabilities of the olfactory system.With their advantages of being able to express various neurotrophic factors,promote axon extension and reorganization of glial scar,OEC transplantation has emerged as a potential strategy to promote repair following SCI.Although OECs have been successfully used in many transplantation experiments with encouraging outcomes,the key factors guiding transplanted OEC homing to the damaged area after SCI remains unclear.Moreover,the directed migration of OECs is thought to account for their ability to ultimately aid in the repair of SCI.Lysophosphatidic acid(LPA),a bioactive lipid mediator,is involved in a wide range of biological response including those mediating the cell cycle,wound healing,and chemotaxis.LPA-induced signals are primarily mediated by G protein-coupled receptors(GPCRs)referred to as LPARl-6.Multiple overlapping or distinct signal transduction pathways including the small GTPases Ras and Rho,and protein kinases including mitogen-activated protein kinase(MAPKs),phosphatidylinositol 3-kinase(PI3K),and protein kinase C(PKC),are triggered through coupling to diverse G proteins in response to LPA.One study found that LPA influenced the migration,proliferation,and cytoskeleton assembly of OECs via ERKI/2 signaling.?-catenin is a transcriptional coregulator of the Wnt signaling pathway that regulates cell fate decisions during embryogenesis.?-catenin signaling-activated OECs are more effective in promoting synaptogenesis,and can enhance axonal regeneration.However,the association between ?-catenin and LPA signaling in OECs migration remains poorly understood.Considering the clinical potential of OECs to remyelinate demyelinated axons,elucidation of the signaling mechanisms involved in mediating its chemotaxis is especially important.We noted that OECs exhibited dose-dependent migration in the presence of LPA by Boyden chamber assay.Expression of LPA receptors in OECs was further detected by real-time quantitative PCR,revealing LPAR1 to be the primary receptor expressed on OECs.To confim the role of LPAR1 in LPA-stimulated migration,OECs were pretreated with Kil6425(an LPAR1/3 antagonist),and their migratory responses to LPA in the absence or presence of inhibitors were examined.The results showed that Ki 16425 markedly diminished the LPA-induced migration of OECs.To fturther clarify the role of LPAR1,shRNA lentiviruses was transfected into OECs in order to speciflcally disrupt LPAR1,suggesting that LPAR1 mediates LPA-induced OECs migration.To verify the sensitization of p-catenin signaling pathway,Western blot showed that the expression of active-p-catenin(ABC)and p-catenin proteins in OEC increased significantly at different time after LPA treatment,and the downstream target genes Tiaml,Runx2 and C-Myc were also significantly activated,which indicated that LPA could activate p-catenin signal in OEC.In order to investigate whether the activation of p-catenin pathway mediates LPA-induced OEC migration,we constructed shRNA lentiviral infected cells specifically interfering with beta-eatenin,and found that the chemotaxis of OEC to LPA was significantly reduced.The results showed that beta-catenin signal is involved in LPA-induced OEC migration.Moreover,silencing LPAR1 not only abolished the migration of OECs but also prevented ERK1/2 phosphorylation and ?-catenin activation,suggesting that LPARI ligation serves to activate the ERK1/2 and ?-catenin pathways in LPA-induced OEC chemotactic migration.Finally,the expression of LPA was significantly increased within two weeks in rat after spinal cord injury.In vivo cell transplantation experiments confirmed that endogenous LPA produced at the site of injury was a key chemokine to promote OECs homing to the lesion site.Collectively,our data provide a further description of the homing effects of LPA and a mechanism by which transplanted OECs migrate to the injured area after SCI in rats,thus providing a strong theoretical basis for better application of OECs in the treatment of SCI.