The role of dietary arachidonic acid and docosahexaenoic acid in preventing the phenotype observed with highly unsaturated fatty acid deficiency

The physiological roles of highly unsaturated fatty acids (HUFA), mainly arachidonic acid (AA, 20:4ω6) and docosahexaenoic acid (DHA, 22:6ω3), are not completely understood. In order to study specific functions for AA and DHA, a delta-6 desaturase knockout (D6D-/-) mouse was created. D6D is a key enzyme in synthesizing HUFA from the precursor dietary essential fatty acids, linoleic acid (LA, 18:2ω6) or α-linolenic acid (ALA, 18:3ω3). By disrupting D6D expression, LA and ALA provided in the diet will not be metabolized to HUFA. Phenotype of the D6D-/mouse is therefore specific to lack of AA and/or DHA and consists of ulcerative dermatitis, male infertility, gastrointestinal ulcers, and hepatic lipidosis. New insight on specific AA and DHA roles was established through dietary prevention of HUFA deficiency phenotype. The absence of a D6D isozyme had to be assessed before further characterizing HUFA roles with the D6D-/mouse model. The presence of a D6D isozyme would interfere with the creation of HUFA deficiency. The primary D6D isozyme candidate was Fads3 gene due to its increased gene expression in D6D-/liver and homology to the Fads2 gene that encodes for D6D. Cloning and transfection of Fads3 into cultured HEK293 cells confirmed lack of D6D activity (Chapter 3). The order of appearance of D6D-/phenotype due to HUFA deficiency had yet to be determined. A D6D-/time course study (Chapter 4) characterized the mouse at different ages in order to follow sequence of HUFA deficiency pathology. The amount of HUFA in D6D-/at weaning was comparable to control mouse indicating the presence of HUFA stores that most likely result from HUFA passed on from the mother. Subsequent HUFA depletion with age correlated with severity of D6D-/phenotype. Male infertility, gastrointestinal erosions, and

高度不饱和脂肪酸（HUFA），主要是花生四烯酸（AA，20:4ω6）和二十二碳六烯酸（DHA，22:6ω3）的生理作用尚未完全明确。为了研究AA和DHA的特定功能，创建了一种Δ - 6去饱和酶基因敲除（D6D - / -）小鼠。D6D是从前体膳食必需脂肪酸亚油酸（LA，18:2ω6）或α - 亚麻酸（ALA，18:3ω3）合成HUFA的关键酶。通过破坏D6D的表达，饮食中提供的LA和ALA将不会被代谢为HUFA。因此，D6D - / -小鼠的表型是缺乏AA和/或DHA所特有的，包括溃疡性皮肤炎、雄性不育、胃肠道溃疡和肝脂肪变性。通过饮食预防HUFA缺乏表型，对AA和DHA的特定作用有了新的认识。在使用D6D - / -小鼠模型进一步描述HUFA的作用之前，必须评估是否不存在D6D同工酶。D6D同工酶的存在会干扰HUFA缺乏状态的形成。由于其在D6D - / -肝脏中基因表达增加以及与编码D6D的Fads2基因具有同源性，主要的D6D同工酶候选基因是Fads3基因。将Fads3基因克隆并转染到培养的HEK293细胞中，证实其缺乏D6D活性（第3章）。由于HUFA缺乏导致的D6D - / -表型出现的顺序尚未确定。一项D6D - / -时间进程研究（第4章）对不同年龄的小鼠进行了特征描述，以追踪HUFA缺乏病理的发展顺序。断奶时D6D - / -小鼠体内的HUFA含量与对照小鼠相当，这表明存在HUFA储备，很可能是来自母体传递的HUFA。随着年龄增长，后续HUFA的消耗与D6D - / -表型的严重程度相关。雄性不育、胃肠道糜烂以及……