Molecular Genetics of Age-Dependent Retinal Degeneration

描述（由申请人提供）：我们的长期目标是了解导致与人类视网膜疾病和衰老相关的视网膜缺陷的分子机制。最近的研究表明，在衰老和一些视网膜退行性疾病中通常观察到类似的突触异常和感光细胞的逐渐丧失。在衰老和年龄依赖性视网膜退行性疾病中观察到的视网膜异常的相似性表明这些疾病背后的分子机制之间存在联系。因此，阐明导致常见的年龄依赖性视网膜异常的分子机制，应该提高我们对年龄依赖性视网膜疾病和视网膜老化的理解。我们确定了一个ENU诱导的突变小鼠品系，FUN 025，显示早期发病的年龄依赖性异常的视网膜。这些小鼠的表型模拟在正常老化视网膜中观察到的异常，但它们出现在较早的时间点。此外，我们发现FUN 025小鼠的视网膜对氧化应激更敏感，这表明FUN 025基因参与保护感光细胞免受氧化应激。在对FUN025突变进行基因定位后，我们发现了跨膜蛋白135（Tmem135）基因中的一个剪接位点突变，该突变位于最小FUN025区域。我们进一步确定TMEM135蛋白定位于光感受器细胞的线粒体以及突触囊泡，并且其表达在正常老化视网膜中减少。线粒体被认为是细胞中氧化损伤的来源和靶点，以及凋亡细胞死亡的介体，并且是受FUN 025突变影响的可能细胞器。这些发现使我们假设FUN 025在线粒体中具有保护感光细胞免受氧化应激的主要作用。在这个应用程序中，我们的主要重点是确定参与年龄依赖性视网膜异常的基因，并表征这些分子。更具体地说，在目标1中，我们将测试Tmem 135作为FUN 025的强候选基因，并明确鉴定负责FUN 025表型的基因。目的2：研究FUN 025在线粒体功能和细胞对氧化应激反应中的作用。此外，我们将测试FUN 025基因的过表达是否能更好地保护感光细胞免受氧化应激。在目标3中，我们将进行另一种小鼠突变体的负责基因的定位克隆，该突变体显示出与FUN 025小鼠中观察到的相同的年龄依赖性感光细胞变性和突触异常。完成拟议的研究应提供多个切入点的分子机制，潜在的年龄依赖性视网膜变性，并可能提供治疗策略，预防视网膜疾病与衰老和年龄依赖性视网膜疾病。

DESCRIPTION (provided by applicant): Our long-term goal is to understand the molecular mechanisms causing retinal defects associated with human retinal diseases and aging. Recent studies have shown that similar synaptic abnormality and gradual photoreceptor cell loss are commonly observed in aging and a number of retinal degenerative diseases. The similarity of retinal abnormalities observed in aging and age-dependent retinal degenerative diseases suggests the link between molecular mechanisms underlying these conditions. Elucidating the molecular mechanisms causing the common age-dependent retinal abnormalities, therefore, should enhance our understanding of age-dependent retinal diseases and aging of the retina. We identified an ENU-induced mutant mouse strain, FUN025, showing early onset of age-dependent abnormalities in the retina. The phenotypes of these mice mimic abnormalities that are observed in normal aging retina, but they appear at the earlier time point. Furthermore, we found that the retina of FUN025 mice is more susceptible to oxidative stress, suggesting that the FUN025 gene is involved in protection of photoreceptor cells from oxidative stress. Following genetic mapping of the FUN025 mutation, we found a splice-site mutation in the transmembrane protein 135 (Tmem135) gene that is in the minimal FUN025 region. We further determined that the TMEM135 protein is localized to mitochondria as well as synaptic vesicles of photoreceptor cells, and its expression is reduced in the normal aging retina. Mitochondria are known as both the source and the target of oxidative damage in cells, as well as the mediator of apoptotic cell death, and are the likely organelle affected by the FUN025 mutation. These findings have led us to our hypothesis that FUN025 has a major role in the mitochondria to protect photoreceptor cells from oxidative stress. In this application, our major focus is to identify genes involved in age-dependent retinal abnormalities, and characterize those molecules. More specifically, in Aim 1, we will test Tmem135 as a strong candidate gene for FUN025, and definitively identify the gene responsible for FUN025 phenotypes. In Aim 2, we will study the role of FUN025 in the mitochondrial functions and cellular responses to oxdative stress. In addition, we will test whether overexpression of the FUN025 gene provides greater protection of photoreceptor cells from oxidative stress. In Aim 3, we will conduct positional cloning of the responsible gene for another mouse mutant showing age-dependent photoreceptor degeneration and synaptic abnormalities, that are identical to those observed in FUN025 mice. Completion of the proposed studies should provide multiple entry points into the molecular mechanisms underlying age-dependent retinal degeneration, and may offer therapeutic strategies for prevention of retinal conditions associated with aging and age-dependent retinal disorders.