Defining the Mechanism of Altered Very Long Chain Fatty Acid Metabolism in Neuro-Ichthyotic Disorders.

超长链脂肪酸-4(ELOVL4)基因的延长突变会导致神经鱼鳞病，其特征是皮肤干燥(鱼鳞病)、认知障碍、癫痫发作和与年龄相关的小脑变性。ELOVL4是调节超长链(VLC28)、饱和脂肪酸(≥-SFA)和多不饱和脂肪酸(VLC-PUFA)生物合成的重要酶，这些脂肪酸统称为甚长链脂肪酸。ELOVL4在特定的组织中表达，在这些组织中，它对VLC-SFA和/或VLC-PUFA的生物合成表现出组织特异性的选择性。在皮肤、脑和眉板腺中，ELOVL4主要产生VLC-SFA，而在视网膜和睾丸中则主要产生VLC-PUFA。然而，一个组织产生VLC-SFA和另一个组织产生VLC-PUFA的机制以及这些VLC-FA如何在每个组织中发挥重要的保护作用仍不清楚。考虑到ELOVL4突变影响皮肤和神经组织的事实，答案肯定是不同突变蛋白的固有酶活性，或者突变蛋白对WT酶合成的VLC-FA的质量和数量的显性负面影响。该建议的目的是研究哪些因素决定了VLC-SFA生物合成相对于VLC-PUFA的组织特异性选择性，以及突变的ELOVL4如何改变这些因素从而导致不同的组织特异性疾病。为了实现他的目标，我们建立了第一个ELOVL4突变的Long Evans大鼠模型(C.736T&gt；G，p.W246G)，该突变导致脊髓小脑性共济失调34(SCA34)并伴有变异性红细胞性角化病(EKV)。与野生型对照大鼠相比，杂合子和纯合子SCA34大鼠从出生起就出现皮肤损害，后来表现出典型的人类疾病的小脑功能障碍迹象19。皮肤VLC-SFA分析表明，与WT对照组相比，纯合子KI组织仅占VLC-SFA总量的33%。这些发现表明，该突变SCA34模型中的神经鱼鳞病病理可能是由于ELOVL4突变引起的皮肤和神经元VLC-FA水平降低所致。我们假设，组织特异性因素决定了VLC-FA的类型(饱和还是多不饱和)，在SCA34患者中发现的皮肤和小脑病理缺陷是由于突变的ELOVL4酶影响了野生型ELOVL4‘S合成VLC-FA的能力。我们提出了两个具体的目标来检验这一假设。在成功完成拟议的实验后，我们将回答尚未解决的问题，即不同的突变ELOVL4蛋白如何影响VLC-FA的生物合成，从而导致神经鱼鳞病。我们预计这将使我们能够在未来的研究中寻求实验性治疗方案，这些研究可能会迅速进入治疗一些人类突变ELOVL4疾病的人类临床试验。

Mutations in the Elongation of Very Long Chain Fatty Acids-4 (ELOVL4) gene cause neuro-ichthyotic disorder characterized by dry scaly skin (ichthyosis) and cognitive deficits, seizures and age-related cerebellar degeneration. ELOVL4 is an essential enzyme that mediates biosynthesis of very long chain (≥C28) saturated (VLC-SFA) and polyunsaturated fatty acids (VLC-PUFA) that are collectively called very long chain fatty acids (VLC-FA). ELOVL4 is expressed in specific tissues in which it exhibits tissue-specific selectivity towards VLC- SFA and/or VLC-PUFA biosynthesis. In the skin, brain and Meibomian glands, ELOVL4 makes mainly VLC- SFA, while in the retina and testes it makes VLC-PUFA. However, the mechanisms by which one tissue makes VLC-SFA and the other VLC-PUFA, and how these VLC-FA exert their important protective roles in each tissue, remain unknown. Considering the fact that mutations in ELOVL4 affect skin and neuronal tissues, the answer must be in either the innate enzyme activity of the different mutant proteins or in a dominant negative effect of the mutant proteins on the quality and quantity of VLC-FA synthesized by the WT enzyme. The objective of this proposal is to examine what factors determine the tissue-specific selectivity of VLC-SFA biosynthesis relative to VLC-PUFA and how mutant ELOVL4 alters such factors to cause the different tissue- specific disorders. To achieve his goal, we generated the first Long Evans rat model of ELOVL4 mutation (c.736T>G, p.W246G) that causes Spinocerebellar ataxia 34 (SCA34) with Erythrokeratodermia variabilis (EKV). Compared to wild type control rats, heterozygous and homozygous SCA34 rats developed skin lesions from birth and later showed signs of cerebellar dysfunction typical of the human disease19. Analysis of skin VLC-SFA showed that the homozygous KI tissue had only about 33% of total VLC-SFA compared to WT controls. These findings indicate that the neuro-ichthyotic pathology in this mutant SCA34 model is likely caused by decreased skin and neuronal VLC-FA levels, an effect of the ELOVL4 mutation. We hypothesize that tissue-specific factors determine which type of VLC-FA (saturated versus polyunsaturated) is made and that the skin and cerebellar pathological defects found in SCA34 patients result from effects of the mutant ELOVL4 enzyme on the wild type ELOVL4’s ability to synthesize VLC-FA. We propose two specific aims to test this hypothesis. Upon successful completion of the proposed experiments, we will answer unresolved questions of how the different mutant ELOVL4 proteins affect VLC-FA biosynthesis to cause neuro-ichthyotic disorders. We anticipate this will allow us to pursue experimental treatment options in future studies which could progress rapidly into human clinical trials for treating some of the human mutant ELOVL4 disorders.