title: Spatial and temporal changes in promoter activity of the astrocyte glutamate transporter GLT1 following traumatic spinal cord injury.
abstract: After traumatic spinal cord injury (SCI), there is an opportunity for preserving function by attenuating secondary cell loss. Astrocytes play crucial roles in the adult CNS and are responsible for the vast majority of glutamate buffering, potentially preventing excitotoxic loss of neurons and oligodendrocytes. We examined spatial and temporal changes in gene expression of the major astrocyte glutamate transporter GLT1 following moderate thoracic contusion SCI using transgenic BAC-GLT1-eGFP promoter reporter mice. In dorsal column white matter, total intensity of GLT1-eGFP expression per region was significantly reduced following SCI at both lesion epicenter and at rostral and caudal areas where no tissue loss occurred. This regional decrease in GLT1 expression was due to significant loss of GLT1-eGFP(+) cells, partially accounted for by apoptosis of eGFP(+) /GFAP(+) astrocytes in both white and gray matter. There were also decreased numbers of GLT1-eGFP-expressing cells in multiple gray matter regions following injury; nevertheless, there was sustained or even increased regional GLT1-eGFP expression in gray matter as a result of up-regulation in astrocytes that continued to express GLT1-eGFP. Although there were increased numbers of GFAP(+) cells both at the lesion site and in surrounding intact spinal cord following SCI, the majority of proliferating Ki67(+) /GFAP(+) astrocytes did not express GLT1-eGFP. These findings demonstrate that spatial and temporal alterations in GLT1 expression observed after SCI result from both astrocyte death and gene expression changes in surviving astrocytes. Results also suggest that following SCI a significant portion of astrocytes lacks GLT1 expression, possibly compromising the important role of astrocytes in glutamate homeostasis.
authors.affiliation: Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: Angelo C
authors.initials: AC
authors.lastname: Lepore
authors.forename: John
authors.initials: J
authors.lastname: O'Donnell
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Bonner
authors.forename: Courtney
authors.initials: C
authors.lastname: Paul
authors.forename: Mark E
authors.initials: ME
authors.lastname: Miller
authors.forename: Britta
authors.initials: B
authors.lastname: Rauck
authors.forename: Robert A
authors.initials: RA
authors.lastname: Kushner
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Rothstein
authors.forename: Itzhak
authors.initials: I
authors.lastname: Fischer
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Maragakis
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000378:metabolism* / Q000473:pathology; D049109:Cell Proliferation; D002470:Cell Survival / Q000235:genetics; D004195:Disease Models, Animal; D027342:Excitatory Amino Acid Transporter 2 / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D018698:Glutamic Acid / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D011401:Promoter Regions, Genetic / Q000235:genetics*; D013116:Spinal Cord / Q000378:metabolism* / Q000473:pathology; D013119:Spinal Cord Injuries / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D013997:Time Factors
chemical_list: D027342:Excitatory Amino Acid Transporter 2; C493396:Slc1a2 protein, mouse; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D018698:Glutamic Acid