טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentShirit Yaniv
SubjectGlucocorticoid - Norepinephrine Interactions at the Level of
Intracellular Signaling: Implications to the
Plasticity Hypothesis of Major
Depression and its Treatment
DepartmentDepartment of Medicine
Supervisors Full Professor Ben-Shachar Dorit
Professor Emeritus Klein Ehud
Full Thesis textFull thesis text - English Version


Abstract

The plasticity hypothesis of major depression states that the stress hormone glucocorticoid (GC) may be detrimental to cellular plasticity and that monoamines, and anti-depressants, may reconstitute this plasticity. Given the key roles norepinephrine (NE) and GCs play in stress and depression, our main aim was to search for a shared NE and GC intracellular pathway affecting plasticity with relevance to depression and its treatment. The plasticity effects of GCs and NE were studied using SH-SY5Y neuroblastoma cells, focusing on morphological effects as well as on L1, laminin, Gap-43, and CREB, genes implicated in neuronal plasticity. Cells were treated with dexamethasone (DEX, a synthetic glucocorticoid receptor agonist) and/or NE. Long-term DEX treatment caused a decrease in neurite length and number, opposite to the effect of NE. DEX treated cells also exhibited a reduction in the expression of Gap-43, L1 and laminin, in the transcription factor CREB as well as in the active phosphorylated CREB (pCREB). NE caused an increase in pCREB, laminin and L1. Cells co-treated with NE and DEX showed intermediate differentiation between control and NE treated cells, observed both morphologically and in gene expression. Therefore, DEX treated cells are less differentiated, NE cells are more differentiated, and NE and GC oppositely affect the same genes, suggesting a common pathway. All the abovementioned genes can be modulated by the transcription factor AP-1 (c-Jun/c-Fos) which may be activated by the MAPK pathway ERK1/2. NE can activate AP-1 via activation of MAPK while GCs can inhibit AP-1 via disruption of AP-1 DNA binding. Both ERK and c-Jun were activated following NE treatment. Co-administration caused hyperactivation of p-ERK, p-c-Jun and c-Fos as compared to control and NE treated cells. This was accompanied by an increase in AP-1 transcriptional activity by both NE and co-treatment. Co-treatment also induced prolonged activation in ERK, Jun and AP-1 activity. DEX did not affect these parameters. pCREB was also hyperactivated by co-treatment, and decreased by DEX, in an ERK independent manner. Altered regulation of the α2-adrenergic receptor (AR) can account for these effects. After 2h of treatment with NE, β-arrestin, a protein involved in receptor desensitization, was co-localized with the α2-AR at the plasma membrane while following co-treatment, β-arrestin was diffuse within the cell. This interaction between DEX and NE may be necessary for the beneficial effects of anti-depressants and further research into this interaction may provide insight into the mechanism of action of anti-depressants.