유전자 조작 마우스를 이용한 O-GlcNAcase와 phospholipase C-gamma1의 생리학적 및 병리생리학적 기능 연구

Abstract

Genetically modified mouse models have emerged as an excellent approach to provide insight into gene regulation, development, pathogenesis, and the treatment of disease. Here, I generated gene-trapped knockout and conditional knockout mice to investigate physiological and pathophysiologcal functions of O-GlcNAcase (OGA) and phospholipase C gamma 1(PLC-gamma1) respectively. O-GlcNAcylation is a posttranslational modification that influences fundamental functions of proteins by regulating protein-protein interactions, altering protein stability, and changing protein activity. O-GlcNAc addition and removal from the Ser and Thr residues of proteins is catalyzed by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. Many studies have directly linked dysregulation of O-GlcNAc cycling to chronic diseases of aging including diabetes, cardiovascular disease, neurodegenerative disorders, and cancer. Using OGA knockout mice, here I propose an important role for O-GlcNAc cycling by OGA in embryonic development and the regulation of the maintenance of genomic stability linked to the aging process. Further investigation using OGA-haploinsufficient mice demonstrated that increased O-GlcNAc level in colon tissues aggravates intestinal inflammation in mouse model of dextran sulfate sodium-induced colitis and colitis-associated caner model by modulating NF-B signaling. Phosphoinositide-specific phospholipase C (PLC) hydrolyzes phosphatidylinositol-4, 5-bisphosphate (PIP2) to inositol-1, 4, 5-triphosphate (IP3) and diacylglycerol (DAG) during ligand-mediated signal transduction. DAG activates protein kinase C (PKC), while binding of IP3 to its receptor triggers the release of calcium ions from intracellular stores. In brain, PLC-gamma1 forms an integral part of neural networks that control disparate brain functions, such as mood and motor activity. Significantly, patients with bipolar disorder who respond well to the lithium prophylaxis have a higher frequency of a polymorphism in the gene on chromosome 20 encoding PLC-gamma1. However, the in vivo role of PLC-gamma1 has not yet been demonstrated. To investigate the physiological of phospholipase C gamma 1(PLC-gamma1), forebrain-specific PLC-gamma1 knockout mice were generated by crossing conditional PLC-gamma1 knockout mice with CaMKII-cre transgenic mice. Here, I show that PLC-gamma1 deletion shows elevated expression of tyrosine hydroxylase, a rate-limiting enzyme in the dopamine biosynthesis pathway, in midbrain and striatum. Correlatively, forebrain-specific PLC-gamma1 knockout mice display hyper-locomotor activity, defects in learning and memory, and robustly aggressive behavior compared to WT control mice. Based on these results, I propose that PLC-gamma1 may be involved in mental disorders related to dopamine neurotransmission including bipolar disorder, attention deficit hyperactivity disorder, and schizophrenia.