Tammimaki A, Aonurm-Helm A, Zhang F P, Poutanen M, Duran-Torres G, Garcia-Horsman A, Mannisto P T
Division of Pharmacology and Pharmacotherapy, Faculty of Pharmacy, University of Helsinki, Finland.
Division of Pharmacology and Toxicology, Institute of Biomedicine and Translational Medicine, Faculty of Medicine, University of Tartu, Estonia.
J Physiol Pharmacol. 2016 Dec;67(6):827-842.
Catechol-O-methyltransferase (COMT) has two isoforms: soluble (S-COMT), which resides in the cytoplasm, and membrane-bound (MB-MT), anchored to intracellular membranes. COMT is involved in the O-methylation of L-DOPA, dopamine and other catechols. The exact role of MB-COMT is still mostly unclear. We wanted to create a novel genetically modified mouse model that specifically lacks MB-COMT activity and to study their behavioral phenotype. MB-COMT knock-in mutant mice were generated by introducing two point mutations in exon 2 of the Comt gene (ATGCTG->GAGCTC disabling the function of the P2 promoter and allowing only the P1-regulated S-COMT transcription. The first mutation changes methionine to glutamic acid whereas the second one does not affect coding. The expression of the two COMT isoforms, total COMT activity in several areas of the brain and peripheral tissues and extracellular dopamine concentrations after L-DOPA (10 mg/kg) and carbidopa (30 mg/kg) subcutaneous administration were assessed. A battery of behavioral tests was performed to compare MB-COMT deficient mice and their wild type littermates of both sexes. MB-COMT deficient mice were seemingly normal, bred usually and had unaltered COMT activity in the brain and periphery despite a complete lack of the MB-COMT protein. MB-COMT deficient male mice showed higher extracellular dopamine levels than their wild-type littermates in the striatum, but not in the mPFC. In addition, the MB-COMT deficient male mice exhibited a distinct endophenotype characterized by schizophrenia-related behaviors like aggressive behavior and reduced prepulse inhibition. They also had prolonged immobility in the tail suspension test. Both sexes were sensitized to acute pain and had normal motor activity but disturbed short-term memory. Hence the behavioral phenotype was not limited to schizophrenia-related endophenotype and some behavioural findings were not sex-dependent. Our findings indicate that MB-COMT is critical for behavior, and its function in COMT-dependent brain areas cannot be entirely substituted by the remaining S-COMT.
儿茶酚-O-甲基转移酶（COMT）有两种亚型：可溶性（S-COMT），位于细胞质中；膜结合型（MB-MT），锚定在细胞内膜上。COMT参与左旋多巴、多巴胺和其他儿茶酚的O-甲基化。MB-COMT的确切作用仍大多不清楚。我们想创建一种新型基因改造小鼠模型，该模型特异性缺乏MB-COMT活性，并研究其行为表型。通过在Comt基因的外显子2中引入两个点突变（ATGCTG->GAGCTC）来产生MB-COMT基因敲入突变小鼠，这会使P2启动子功能丧失，仅允许P1调控的S-COMT转录。第一个突变将甲硫氨酸变为谷氨酸，而第二个突变不影响编码。评估了两种COMT亚型的表达、大脑和外周组织几个区域的总COMT活性以及皮下注射左旋多巴（10mg/kg）和卡比多巴（30mg/kg）后的细胞外多巴胺浓度。进行了一系列行为测试以比较MB-COMT缺陷小鼠及其野生型同窝仔鼠的两性情况。MB-COMT缺陷小鼠看似正常，繁殖正常，尽管完全缺乏MB-COMT蛋白，但大脑和外周的COMT活性未改变。MB-COMT缺陷雄性小鼠纹状体中的细胞外多巴胺水平高于其野生型同窝仔鼠，但内侧前额叶皮质中则不然。此外，MB-COMT缺陷雄性小鼠表现出一种独特的内表型，其特征为与精神分裂症相关的行为，如攻击行为和前脉冲抑制降低。它们在悬尾试验中的不动时间也延长。两性对急性疼痛均敏感，运动活动正常，但短期记忆受到干扰。因此，行为表型不限于与精神分裂症相关的内表型，且一些行为发现不存在性别依赖性。我们的研究结果表明，MB-COMT对行为至关重要，其在依赖COMT的脑区中的功能不能完全被剩余的S-COMT替代。
