Essential Role of Very Long Chain Fatty Acids in Retinal Function

摘要 超长链脂肪酸(VLC-FA，≥C28)是通过超长链脂肪酸的延伸而合成的 酸-4(ELOVL4)酶，是生命所必需的，因此组织VLC-FA的耗竭(由于敲除 ELOVL4)会导致新生儿死亡。ELOVL4蛋白在视网膜、眉板腺、脑、 皮肤和睾丸。在每一种组织中，这种酶都会产生两种不同的VLC-FA。有一门课是 VLC-饱和脂肪酸(VLC-SFA)，主要存在于皮肤、大脑、眉毛腺和泪膜中。 另一种是VLC多不饱和脂肪酸(VLC-PUFA)，存在于视网膜、睾丸和精子中。自.以来 VLC-FA对于这些组织的正常功能是必不可少的，ELOVL4的突变导致不同的组织- 特殊疾病，如Stargardt样黄斑营养不良(STGD3)、脊髓小脑性共济失调-34(SCA34)、皮肤 病理、癫痫发作和死亡。然而，一个组织主要制造VLC-SFA和 其他VLC-PUFA以及VLC-FA如何在每个组织中发挥其重要性仍不清楚。我们寻求 了解这种现象的分子基础，目的是开发治疗靶点 延缓疾病的发展。我们的实验室和其他实验室已经表明，视网膜ELOVL4或 突变体ELOVL4的表达导致影响视网膜结构的VLC-SFA和VLC-PUFA的耗尽 和功能。我们还发现，STGD3突变体ELOVL4缺乏VLC-PUFA的生物合成，并发挥了 体内外对野生型ELOVL4(WT ELOVL4)的显性负效应导致VLC-FA降低 生物合成。这些结果表明，VLC-FA对于维持感光细胞的健康和功能是必要的。 为了了解一组突变如何导致视力丧失和另一组突变如何导致共济失调，我们成功地 建立了SCA34 ELOVL4突变(C.736T&gt；G)的Long Evans(LE)大鼠敲入模型， 重述了人类的混乱。因此，我们现在有了STGD3和SCA34的动物模型。我们 假设特定于组织的因素决定特定组织中产生哪种类型的脂肪酸，并且 在STGD3和SCA34患者中发现的病理差异是由于不同类型的 VLC-FA由突变酶直接产生或由突变酶对VLC-FA的影响产生 由野生型ELOVL4酶产生。我们提出了两个具体目标：1)确定不同之处 表达ELOVL4的组织控制着ELOVL4的VLC-SFA和VLC-PUFA的生物合成活性。2)至 确定不同的ELOVL4突变如何影响它们所产生的VLC-FA的质量和数量 合成。这些结果将提供更好的机制洞察枯竭的相对贡献。 VLC-FA和突变的ELOVL4在突变的ELOVL4疾病进展中的作用。这可能会潜在地 通过为开发潜在的治疗方法铺平道路，立即产生积极影响 来拯救这些疾病。

Abstract Very long chain fatty acids (VLC-FA, ≥ C28) are synthesized by the Elongation of Very Long Chain Fatty Acids-4 (ELOVL4) enzyme and are essential for life such that depletion of tissue VLC-FA (due to knockout of ELOVL4) causes neonatal lethality. The ELOVL4 protein is expressed in the retina, Meibomian glands, brain, skin, and testes. In each of these tissues, the enzyme makes two different classes of VLC-FA. One class is VLC-saturated fatty acids (VLC-SFA) that are found mainly in the skin, brain, Meibomian glands and tear film. The other is VLC-polyunsaturated fatty acids (VLC-PUFA) that are found in the retina, testes and sperm. Since VLC-FA are essential for the normal function of these tissues, mutations in ELOVL4 cause distinct tissue- specific disorders like Stargardt-like macular dystrophy (STGD3), spinocerebellar ataxia-34 (SCA34), skin pathologies, seizures and death. However, the mechanisms by which one tissue makes mainly VLC-SFA and the other VLC-PUFA, and how the VLC-FA exert their importance in each tissue remain unknown. We seek to understand the molecular basis of this phenomenon with the goal of developing therapeutic targets for attenuating disease progression. Our lab and others have shown that conditional deletion of retinal Elovl4 or expression of the mutant Elovl4 leads to depletion of VLC-SFA and VLC-PUFA, which affect retinal structure and function. We also showed that the STGD3 mutant ELOVL4 lacks VLC-PUFA biosynthesis and exerts a dominant negative effect on wild type ELOVL4 (WT ELOVL4) in vitro and in vivo causing decreased VLC-FA biosynthesis. These suggest that VLC-FA are necessary for maintenance of photoreceptor health and function. To understand how one set of mutations causes vision loss and another causes ataxia, we successfully generated a Long Evans (LE) rat knock-in model of the SCA34 ELOVL4 mutation (c.736T>G) that recapitulates the human disorder. Consequently, we now have animal models of STGD3 and SCA34. We hypothesize that tissue-specific factors determine which type of fatty acid is made in specific tissues and that the pathological differences found in patients with STGD3 and SCA34 result from differences in the types of VLC-FAs produced directly by the mutant enzymes or from effects of the mutant enzymes on VLC-FA produced by the wild type ELOVL4 enzyme. We propose two specific aims: 1) To determine how different ELOVL4-expressing tissues control the VLC-SFA and VLC-PUFA biosynthetic activity of ELOVL4. 2) To determine how the different ELOVL4 mutations affect the quality and quantity of the VLC-FA that they synthesize. The results would provide better mechanistic insight into the relative contributions of the depletion of VLC-FA and the mutant ELOVL4 in the progression of the mutant ELOVL4 disorders. This could potentially provide an immediate positive impact by paving the way for development of potential therapeutic approaches to rescue these disorders.