Date of Degree

2-2019

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biochemistry

Advisor

Eitan Friedman

Committee Members

Rene Hen

Jesus Angulo

Itzhak Mano

Kaliris Salas-Ramirez

Subject Categories

Behavioral Neurobiology | Biochemistry | Enzymes and Coenzymes | Molecular and Cellular Neuroscience | Molecular Biology | Nervous System Diseases

Keywords

anxiety, depression, 5-HT4, CK2, antidepressants, serotonin

Abstract

The serotonergic system has been the major candidate in the pathophysiology of mood related disorders such as anxiety and major depressive disorder (MDD). Unfortunately, current antidepressant drugs are ineffective in 50% of the population and require chronic administration for a period of 3-6 weeks before the onset of therapeutic response. 5-HT4 receptor (5-HT4R) agonists have emerged as potential candidates for fast antidepressant action, since an antidepressant response can be achieved after 3 days of pharmacological administration in rodents.

This dissertation aims to investigate the role of casein kinase 2 (CK2) as a regulator of 5-HT4R expression and activity using in vitro techniques and in vivo mouse models. We present evidence, in two different CK2α conditional knockout (KO) mouse lines, that CK2 regulation of 5-HT4R is region specific in the brain. When CK2α is ablated, 5-HT4R mRNA expression is upregulated in the medial PFC (mPFC) but not in other regions where CK2α is also absent like the striatum or the hippocampus. In vitro, 5-HT4R signaling and expression at the plasma membrane is enhanced after shRNA knockdown or pharmacological inhibition of CK2. In vivo, 5-HT4R is also upregulated as evidenced by increased pERK expression in the mPFC that is sensitive to 5-HT4R antagonist treatment, GR113808, of the CK2α KO mice. Behaviorally, the CK2α KO mice present an antidepressed and anxiolytic-like phenotype in a battery of tests of behavioral despair and they are more sensitive to antidepressant treatment when compared to wild-type (WT) littermates. Interestingly, AAV9-mediated knockdown of CK2α in the mPFC of adult mice is sufficient to phenocopy the behavior of the CK2α KO animals. Although AAV9-HTR4-shRNA-mediated reduction of HTR4 expression in the mPFC of CK2α lead only to partial rescue of the phenotype, it was sufficient to overexpress 5-HT4R in the mPFC to generate mice with an antidepressed- and an anxiolytic- like behavior. In addition, AAV9-mediated knockdown of CK2α but not 5-HT4R overexpression lead to increased neurogenesis in the ventral hippocampus. This was paralleled by an impairment in spatial learning and indicated that while the CK2-mediated regulation of 5-HT4R is specific to the mPFC and responsible for the antidepressed and anxiolytic-like phenotype, CK2 might also act through a 5-HT4R-independent mechanism responsible to act on aspects of cognition and neurogenesis.

In summary, my work identifies CK2 as a region-specific negative regulator of 5-HT4R levels and activity and provides evidence that manipulation of CK2 through the upregulation of the 5-HT4R is responsible for mood-related phenotypes and provides a new mechanism of antidepressant action.

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