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Glucocorticoid-dependent hippocampal transcriptome in male rats: pathway-specific alterations with aging.

Chen KC, Blalock EM, Curran-Rauhut MA, Kadish I, Blalock SJ, Brewer L, Porter NM, Landfield PW - Endocrinology (2013)

Bottom Line: Short-term CORT (4 days) did not recapitulate this transcriptome.We then compared the GC transcriptome with a previously defined hippocampal aging transcriptome, revealing a high proportion of common genes.These results contradict the hypothesis that GCs simply promote brain aging and also suggest that the opposite direction shifts during aging reflect resistance to CORT regulation.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Biomedical Pharmacology, University of Kentucky College of Medicine, Lexington, KY 40536, USA.

ABSTRACT
Although glucocorticoids (GCs) are known to exert numerous effects in the hippocampus, their chronic regulatory functions remain poorly understood. Moreover, evidence is inconsistent regarding the long-standing hypothesis that chronic GC exposure promotes brain aging/Alzheimer disease. Here, we adrenalectomized male F344 rats at 15 months of age, maintained them for 3 months with implanted corticosterone (CORT) pellets producing low or intermediate (glucocorticoid receptor-activating) blood levels of CORT, and performed microarray/pathway analyses in hippocampal CA1. We defined the chronic GC-dependent transcriptome as 393 genes that exhibited differential expression between intermediate and low CORT groups. Short-term CORT (4 days) did not recapitulate this transcriptome. Functional processes/pathways overrepresented by chronic CORT-up-regulated genes included learning/plasticity, differentiation, glucose metabolism, and cholesterol biosynthesis, whereas processes overrepresented by CORT-down-regulated genes included inflammatory/immune/glial responses and extracellular structure. These profiles indicate that GCs chronically activate neuronal/metabolic processes while coordinately repressing a glial axis of reactivity/inflammation. We then compared the GC transcriptome with a previously defined hippocampal aging transcriptome, revealing a high proportion of common genes. Although CORT and aging moved expression of some common genes in the same direction, the majority were shifted in opposite directions by CORT and aging (eg, glial inflammatory genes down-regulated by CORT are up-regulated with aging). These results contradict the hypothesis that GCs simply promote brain aging and also suggest that the opposite direction shifts during aging reflect resistance to CORT regulation. Therefore, we propose a new model in which aging-related GC resistance develops in some target pathways, whereas GC overstimulation develops in others, together generating much of the brain aging phenotype.

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Immunohistochemical expression of GRs in dorsal hippocampal field CA1 of F344 rats. A, GR immunostaining showing dense GR nuclear concentration in pyramidal neurons of stratum pyramidale (sp), with less densely stained (predominantly glial) cells distributed throughout the corpus callosum (cc), stratum oriens (so), and stratum radiatum (sr). B, Higher magnification photomicrograph (calibration in C) of GR staining in sp, so, and alveus of the CA1 region, more clearly illustrating lighter staining of the generally smaller nuclei of glial cells compared with neurons of sp. C and D, Double-labeled immunofluorescent images of GR (red) and the specific astrocyte marker, GFAP (green), clarifying glial cell-type localization. C, Arrow points to examples of GR-positive nuclear staining in oligodendrocytes, identified by location and distribution in white matter and the paucity of adjacent GFAP (inset, lower right: magnification of example cells highlighted by the arrow). D, Arrow points to the low-intensity GR fluorescent nucleus in so, adjacent to a formation of GFAP, probably an astrocyte. GR staining here was almost entirely nuclear and because astrocytic GFAP is exclusively cytoplasmic, the 2 proteins exhibited little overlap in merged images (inset, lower right: magnification of an example cell highlighted by the arrow). Compared with glial nuclei, note the bright GR immunofluorescence of neurons in sp. Images have been contrast enhanced.
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Figure 4: Immunohistochemical expression of GRs in dorsal hippocampal field CA1 of F344 rats. A, GR immunostaining showing dense GR nuclear concentration in pyramidal neurons of stratum pyramidale (sp), with less densely stained (predominantly glial) cells distributed throughout the corpus callosum (cc), stratum oriens (so), and stratum radiatum (sr). B, Higher magnification photomicrograph (calibration in C) of GR staining in sp, so, and alveus of the CA1 region, more clearly illustrating lighter staining of the generally smaller nuclei of glial cells compared with neurons of sp. C and D, Double-labeled immunofluorescent images of GR (red) and the specific astrocyte marker, GFAP (green), clarifying glial cell-type localization. C, Arrow points to examples of GR-positive nuclear staining in oligodendrocytes, identified by location and distribution in white matter and the paucity of adjacent GFAP (inset, lower right: magnification of example cells highlighted by the arrow). D, Arrow points to the low-intensity GR fluorescent nucleus in so, adjacent to a formation of GFAP, probably an astrocyte. GR staining here was almost entirely nuclear and because astrocytic GFAP is exclusively cytoplasmic, the 2 proteins exhibited little overlap in merged images (inset, lower right: magnification of an example cell highlighted by the arrow). Compared with glial nuclei, note the bright GR immunofluorescence of neurons in sp. Images have been contrast enhanced.

Mentions: Immunohistochemical analysis was used to assess the distribution and relative concentration of GRs among cell types in the hippocampal field CA1 and adjacent corpus callosum of intact F344 rats (Figure 4). Figure 4, A and B, illustrate that pyramidal neurons exhibited intense GR immunostaining compared with that of glial cells scattered throughout other layers and white matter, as reported previously for rats (88). Double-label immunohistochemical analysis of GR and GFAP showed that nuclei with low GR immunoreactivity were frequently localized adjacent to astroglial cytoplasmic GFAP structures (Figure 4D), identifying them as likely astrocyte nuclei or were not clearly associated with GFAP but instead were aligned in parallel to white matter fibers, identifying them as likely oligodendrocytes (Figure 4C). These findings are consistent with the interpretation that glial cell nuclei contain low concentrations of GR relative to those in neurons (81, 88).


Glucocorticoid-dependent hippocampal transcriptome in male rats: pathway-specific alterations with aging.

Chen KC, Blalock EM, Curran-Rauhut MA, Kadish I, Blalock SJ, Brewer L, Porter NM, Landfield PW - Endocrinology (2013)

Immunohistochemical expression of GRs in dorsal hippocampal field CA1 of F344 rats. A, GR immunostaining showing dense GR nuclear concentration in pyramidal neurons of stratum pyramidale (sp), with less densely stained (predominantly glial) cells distributed throughout the corpus callosum (cc), stratum oriens (so), and stratum radiatum (sr). B, Higher magnification photomicrograph (calibration in C) of GR staining in sp, so, and alveus of the CA1 region, more clearly illustrating lighter staining of the generally smaller nuclei of glial cells compared with neurons of sp. C and D, Double-labeled immunofluorescent images of GR (red) and the specific astrocyte marker, GFAP (green), clarifying glial cell-type localization. C, Arrow points to examples of GR-positive nuclear staining in oligodendrocytes, identified by location and distribution in white matter and the paucity of adjacent GFAP (inset, lower right: magnification of example cells highlighted by the arrow). D, Arrow points to the low-intensity GR fluorescent nucleus in so, adjacent to a formation of GFAP, probably an astrocyte. GR staining here was almost entirely nuclear and because astrocytic GFAP is exclusively cytoplasmic, the 2 proteins exhibited little overlap in merged images (inset, lower right: magnification of an example cell highlighted by the arrow). Compared with glial nuclei, note the bright GR immunofluorescence of neurons in sp. Images have been contrast enhanced.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3713214&req=5

Figure 4: Immunohistochemical expression of GRs in dorsal hippocampal field CA1 of F344 rats. A, GR immunostaining showing dense GR nuclear concentration in pyramidal neurons of stratum pyramidale (sp), with less densely stained (predominantly glial) cells distributed throughout the corpus callosum (cc), stratum oriens (so), and stratum radiatum (sr). B, Higher magnification photomicrograph (calibration in C) of GR staining in sp, so, and alveus of the CA1 region, more clearly illustrating lighter staining of the generally smaller nuclei of glial cells compared with neurons of sp. C and D, Double-labeled immunofluorescent images of GR (red) and the specific astrocyte marker, GFAP (green), clarifying glial cell-type localization. C, Arrow points to examples of GR-positive nuclear staining in oligodendrocytes, identified by location and distribution in white matter and the paucity of adjacent GFAP (inset, lower right: magnification of example cells highlighted by the arrow). D, Arrow points to the low-intensity GR fluorescent nucleus in so, adjacent to a formation of GFAP, probably an astrocyte. GR staining here was almost entirely nuclear and because astrocytic GFAP is exclusively cytoplasmic, the 2 proteins exhibited little overlap in merged images (inset, lower right: magnification of an example cell highlighted by the arrow). Compared with glial nuclei, note the bright GR immunofluorescence of neurons in sp. Images have been contrast enhanced.
Mentions: Immunohistochemical analysis was used to assess the distribution and relative concentration of GRs among cell types in the hippocampal field CA1 and adjacent corpus callosum of intact F344 rats (Figure 4). Figure 4, A and B, illustrate that pyramidal neurons exhibited intense GR immunostaining compared with that of glial cells scattered throughout other layers and white matter, as reported previously for rats (88). Double-label immunohistochemical analysis of GR and GFAP showed that nuclei with low GR immunoreactivity were frequently localized adjacent to astroglial cytoplasmic GFAP structures (Figure 4D), identifying them as likely astrocyte nuclei or were not clearly associated with GFAP but instead were aligned in parallel to white matter fibers, identifying them as likely oligodendrocytes (Figure 4C). These findings are consistent with the interpretation that glial cell nuclei contain low concentrations of GR relative to those in neurons (81, 88).

Bottom Line: Short-term CORT (4 days) did not recapitulate this transcriptome.We then compared the GC transcriptome with a previously defined hippocampal aging transcriptome, revealing a high proportion of common genes.These results contradict the hypothesis that GCs simply promote brain aging and also suggest that the opposite direction shifts during aging reflect resistance to CORT regulation.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Biomedical Pharmacology, University of Kentucky College of Medicine, Lexington, KY 40536, USA.

ABSTRACT
Although glucocorticoids (GCs) are known to exert numerous effects in the hippocampus, their chronic regulatory functions remain poorly understood. Moreover, evidence is inconsistent regarding the long-standing hypothesis that chronic GC exposure promotes brain aging/Alzheimer disease. Here, we adrenalectomized male F344 rats at 15 months of age, maintained them for 3 months with implanted corticosterone (CORT) pellets producing low or intermediate (glucocorticoid receptor-activating) blood levels of CORT, and performed microarray/pathway analyses in hippocampal CA1. We defined the chronic GC-dependent transcriptome as 393 genes that exhibited differential expression between intermediate and low CORT groups. Short-term CORT (4 days) did not recapitulate this transcriptome. Functional processes/pathways overrepresented by chronic CORT-up-regulated genes included learning/plasticity, differentiation, glucose metabolism, and cholesterol biosynthesis, whereas processes overrepresented by CORT-down-regulated genes included inflammatory/immune/glial responses and extracellular structure. These profiles indicate that GCs chronically activate neuronal/metabolic processes while coordinately repressing a glial axis of reactivity/inflammation. We then compared the GC transcriptome with a previously defined hippocampal aging transcriptome, revealing a high proportion of common genes. Although CORT and aging moved expression of some common genes in the same direction, the majority were shifted in opposite directions by CORT and aging (eg, glial inflammatory genes down-regulated by CORT are up-regulated with aging). These results contradict the hypothesis that GCs simply promote brain aging and also suggest that the opposite direction shifts during aging reflect resistance to CORT regulation. Therefore, we propose a new model in which aging-related GC resistance develops in some target pathways, whereas GC overstimulation develops in others, together generating much of the brain aging phenotype.

Show MeSH
Related in: MedlinePlus