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来合成的。 Acids-4（VLC 4）酶是生命所必需的，使得组织VLC-FA的消耗（由于VLC-FA的敲除）导致细胞中VLC-FA的减少。 VL 4）导致新生儿死亡。HPVL 4蛋白在视网膜、睑板腺、脑 皮肤和睾丸在这些组织中的每一个中，酶产生两种不同类型的VLC-FA。一个类 VLC饱和脂肪酸（VLC-SFA）主要存在于皮肤、大脑、睑板腺和泪膜中。 另一种是在视网膜、睾丸和精子中发现的VLC-多不饱和脂肪酸（VLC-PUFA）。以来 VLC-FA对于这些组织的正常功能是必不可少的，VLC-FA中的突变导致不同的组织- 特异性疾病如Stargardt样黄斑营养不良（STGD 3）、脊髓小脑共济失调-34（SCA 34）、皮肤 病理、癫痫和死亡。然而，一种组织主要产生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然未知。我们寻求 了解这种现象的分子基础，目的是开发治疗靶点， 减缓疾病进展。我们的实验室和其他实验室已经表明，视网膜Elovl 4或Elovl 4基因的条件性缺失， 突变体Elov 14的表达导致VLC-SFA和VLC-PUFA的消耗，其影响视网膜结构 和功能我们还表明，STGD 3突变体VL 4缺乏VLC-PUFA的生物合成，并发挥作用。 体外和体内对野生型VL 4（WT VL 4）的显性负效应，导致VLC-FA降低 生物合成这些表明VLC-FA对于维持感光细胞的健康和功能是必需的。 为了了解一组突变如何导致视力丧失，另一组突变如何导致共济失调，我们成功地 产生了SCA 34 ELOVL 4突变（c.736T>G）的Long Evans（LE）大鼠敲入模型， 概括了人类的失调因此，我们现在有了STGD 3和SCA 34的动物模型。我们 假设组织特异性因素决定哪种类型的脂肪酸在特定组织中产生， 在STGD 3和SCA 34患者中发现的病理学差异是由于 由突变酶直接产生的VLC-FA或由突变酶对VLC-FA的作用产生的VLC-FA 由野生型HPVL 4酶产生。我们提出了两个具体目标：1）确定如何不同 表达VL 4的组织控制VL 4的VLC-SFA和VLC-PUFA生物合成活性。2)到 确定不同的VLC 4突变如何影响VLC-FA的质量和数量， 合成。结果将提供更好的机制洞察的相对贡献的耗尽 VLC-FA和突变型VLC-VL 4在突变型VLC-VL 4病症的进展中的作用。这可能会 通过为开发潜在的治疗方法铺平道路，提供直接的积极影响 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.