title: Protein S protects neurons from excitotoxic injury by activating the TAM receptor Tyro3-phosphatidylinositol 3-kinase-Akt pathway through its sex hormone-binding globulin-like region.
abstract: The anticoagulant factor protein S (PS) protects neurons from hypoxic/ischemic injury. However, molecular mechanisms mediating PS protection in injured neurons remain unknown. Here, we show mouse recombinant PS protects dose-dependently mouse cortical neurons from excitotoxic NMDA-mediated neuritic bead formation and apoptosis by activating the phosphatidylinositol 3-kinase (PI3K)-Akt pathway (EC(50) = 26 ± 4 nm). PS stimulated phosphorylation of Bad and Mdm2, two downstream targets of Akt, which in neurons subjected to pathological overstimulation of NMDA receptors (NMDARs) increased the antiapoptotic Bcl-2 and Bcl-X(L) levels and reduced the proapoptotic p53 and Bax levels. Adenoviral transduction with a kinase-deficient Akt mutant (Ad.Akt(K179A)) resulted in loss of PS-mediated neuronal protection, Akt activation, and Bad and Mdm2 phosphorylation. Using the TAM receptors tyrosine kinases Tyro3-, Axl-, and Mer-deficient neurons, we showed that PS protected neurons lacking Axl and Mer, but not Tyro3, suggesting a requirement of Tyro3 for PS-mediated protection. Consistent with these results, PS dose-dependently phosphorylated Tyro3 on neurons (EC(50) = 25 ± 3 nm). In an in vivo model of NMDA-induced excitotoxic lesions in the striatum, PS dose-dependently reduced the lesion volume in control mice (EC(50) = 22 ± 2 nm) and protected Axl(-/-) and Mer(-/-) transgenic mice, but not Tyro3(-/-) transgenic mice. Using different structural PS analogs, we demonstrated that the C terminus sex hormone-binding globulin-like (SHBG) domain of PS is critical for neuronal protection in vitro and in vivo. Thus, our data show that PS protects neurons by activating the Tyro3-PI3K-Akt pathway via its SHGB domain, suggesting potentially a novel neuroprotective approach for acute brain injury and chronic neurodegenerative disorders associated with excessive activation of NMDARs.
authors.affiliation: Center for Neurodegenerative and Vascular Brain Disorders, Department of Neurosurgery and Neurology, University of Rochester Medical Center, Rochester, New York 14642, USA.
authors.forename: Zhihui
authors.initials: Z
authors.lastname: Zhong
authors.forename: Yaoming
authors.initials: Y
authors.lastname: Wang
authors.forename: Huang
authors.initials: H
authors.lastname: Guo
authors.forename: Abhay
authors.initials: A
authors.lastname: Sagare
authors.forename: José A
authors.initials: JA
authors.lastname: Fernández
authors.forename: Robert D
authors.initials: RD
authors.lastname: Bell
authors.forename: Theresa M
authors.initials: TM
authors.lastname: Barrett
authors.forename: John H
authors.initials: JH
authors.lastname: Griffin
authors.forename: Robert S
authors.initials: RS
authors.lastname: Freeman
authors.forename: Berislav V
authors.initials: BV
authors.lastname: Zlokovic
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity; D055785:Gene Knockdown Techniques; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D018696:Neuroprotective Agents / Q000494:pharmacology; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism*; D017293:Protein S / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism* / Q000502:physiology; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
chemical_list: D018690:Excitatory Amino Acid Agonists; D018696:Neuroprotective Agents; D017293:Protein S; D012738:Sex Hormone-Binding Globulin; D058539:Phosphatidylinositol 3-Kinase; D020794:Receptor Protein-Tyrosine Kinases; C513478:Tyro3 protein, mouse; D051057:Proto-Oncogene Proteins c-akt