Abstract

Several reports indicate that the activity of the hypothalamic-pituitary-adrenal axis (HPA) as measured by the increased level of adrenocorticotropic hormone (ACTH), and corticosterone is increased after a brain insult. These hormones are the effectors secreted respectively by the pituitary and adrenal glands. It has been shown that the down-regulation of corticosterone levels can improve detrimental outcomes associated with ischemic brain injuries. Neonatal hypoxia-ischemia (HI) is a devastating perinatal event with a grim prognosis and limited therapeutic strategies. In recent studies, granulocyte-colony stimulating factor (G-CSF) has shown promise in neonatal HI investigations by improving neuromotor function and reducing apoptosis in the brain. Furthermore, G-CSF is shown in the naïve rat to regulate hormones of the HPA axis. Therefore we hypothesized that G-CSF may in part confer its neuroprotective properties by influencing the pituitary-adrenal response after neonatal HI. To test our hypothesis, metyrapone was administered to inhibit the release of rodent specific glucocorticoid, corticosterone, at the adrenal level. Dexamethasone, a synthetic glucocorticoid, was administered to agonize the effects of corticosterone. Following the Rice-Vannucci model, seven-day old rats (P7) were subjected to unilateral carotid ligation followed by 2.5 hours of hypoxia. Our results show that both G-CSF and metyrapone significantly reduced infarct volume via anti-apoptotic properties but lost its protective effect when combined with dexamethasone. Additionally, G-CSF suppressed the increase of corticosterone in the blood after HI. To investigate the mechanism by which G-CSF modulated corticosterone synthesis, we evaluated its effect in adrenal cortical cells in vitro. Our results indicate that G-CSF activated the JAK/PI3K/Akt/PDE3B pathway, which in turn inhibited corticosterone synthesis. The inhibitors of JAK/PI3K/PDE3B respectively Tyrphostin AG490, LY-294002, and 3-isobutyl-1methylxanthine reversed the inhibitory effect of G-CSF on corticosterone synthesis. We report that G-CSF was neuroprotective in neonatal HI by reducing infarct volume, by suppressing the HIinduced increase of the Bax/Bcl-2 ratio, and by decreasing corticosterone at the adrenal level via the JAK/PI3K/PDE3B pathway. Metyrapone was able to confer similar neuroprotection as G-CSF while dexamethasone reversed the effects of G-CSF. In conclusion, we show that reducing corticosterone was neuroprotective after neonatal HI, which can be achieved by administering G-CSF.

LLU Discipline

Microbiology and Molecular Genetics

Department

Basic Sciences

School

School of Medicine

First Advisor

Ashwal, Stephen

Second Advisor

Fletcher, Hansel

Third Advisor

Gridley, Daila

Fourth Advisor

Zhang, John H.

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

January 2012

Date (Title Page)

6-1-2012

Language

English

Subject - Local

Hypothalamic-Pituitary-Adrenal Axis, Neonatal Hypoxia-Ischemia, Neuromotor Function, Brain apoptosis

Type

Dissertation

Page Count

106 p.

Digital Format

Application/PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses & Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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