Quality control mechanisms against misfolded rhodopsins in Drosophila.

描述（由申请人提供）：色素性视网膜炎是一组遗传性疾病，表现为视网膜功能的进行性丧失。常染色体显性视网膜色素变性（ADRP）的最常见原因之一是视紫红质基因突变，破坏了其编码蛋白的折叠特性。我们的长期目标是了解一旦这些视紫红质蛋白在内质网（ER）中合成，细胞如何应对由它们引起的应激。由于大多数细胞具有强大的质量控制机制，可以帮助从ER中消除这种错误折叠的蛋白质，因此更好地了解这些机制可能具有治疗意义。我们专注于两个特定的ER质量控制机制，可以帮助抑制由错误折叠的视紫红质引起的视网膜变性。首先是ER相关降解（ERAD），它是指泛素介导的ER错误折叠蛋白的降解。在果蝇的ADRP模型中，刺激ERAD可以抑制视网膜变性，但其潜在机制仍知之甚少。此外，ADRP可能被ER应激激活的细胞内信号传导途径抑制，称为未折叠蛋白反应（UPR）。UPR的一个中心分支由xbp 1 mRNA在细胞质中的非常规剪接介导，导致活性xbp 1转录因子的合成。xbp1的转录靶点包括ERAD的调节因子。为了研究ERAD和UPR在ADRP动物模型中抑制视网膜变性的机制，我们计划使用经典果蝇遗传学，细胞生物学分析和高通量RNAi测定的组合。具体来说，我们计划调查的确切机制，错误折叠的视紫红质被检测到的ERAD机器和进口到细胞质中的降解。此外，我们计划研究xbp1介导的UPR通路是如何调节的。我们将测试一个特定的假设，其中xbp1 mRNA剪接是由一个特定的磷酸酶调节，而这种磷酸酶反过来又由一个调节亚基，结合到xbp1 mRNA的调节。通过这种方法鉴定的任何新基因或机制将在ADRP的果蝇模型中检查对视网膜变性的可能影响，其中视紫红质编码基因中的内源性突变触发年龄相关性视网膜变性的显性形式。由于果蝇模型显示出与人类状况惊人的相似程度，我们认为这项研究的成功结果可能直接影响人类ADRP新策略的开发。 公共卫生相关性：视紫红质基因的突变导致大约四分之一的常染色体显性形式的视网膜色素变性（ADRP），这是一种导致40~60岁个体失明的遗传性疾病。因此，更好地了解有助于消除错误折叠视紫红质的机制可能对开发针对这种疾病的新治疗策略产生直接影响。

DESCRIPTION (provided by applicant): Retinitis Pigmentosa is a group of inherited disorders that show a progressive loss of retinal function. One of the most common causes of Autosomal Dominant Retinitis Pigmentosa (ADRP) are mutations in the rhodopsin gene that disrupt its encoded protein's folding property. Our long-term goal is to understand how cells respond to stress caused by such rhodopsin proteins once they are synthesized in the endoplasmic reticulum (ER). As most cells have robust quality control mechanisms that can help eliminate such misfolded proteins from the ER, a better understanding of these mechanisms may have therapeutic implications. We focus on two specific ER quality control mechanisms that can help suppress retinal degeneration caused by misfolded rhodopsins. First is ER-Associated Degradation (ERAD), which refers to the ubiquitin-mediated degradation of misfolded proteins from the ER. Stimulation of ERAD can suppress retinal degeneration in a Drosophila model for ADRP, but the underlying mechanism remains poorly understood. In addition, ADRP may be suppressed by an intracellular signaling pathway activated by ER-stress, known as the Unfolded Protein Response (UPR). A central branch of the UPR is mediated by the unconventional splicing of xbp1 mRNA in the cytoplasm, leading to the synthesis of an active xbp1 transcription factor. Among the transcription targets of xbp1 include regulators of ERAD. To investigate mechanisms by which ERAD and the UPR suppress retinal degeneration in animal models of ADRP, we plan to use a combination of classical Drosophila genetics, cell biological analysis and high throughput RNAi assays. Specifically, we plan to investigate the precise mechanism by which misfolded rhodopsins are detected by the ERAD machinery and imported into the cytoplasm for degradation. In addition, we plan to study how the xbp1-mediated UPR pathway is regulated. We will test a specific hypothesis where xbp1 mRNA splicing is modulated by a specific phosphatase, and this phosphatase is in turn regulated by a regulatory subunit that binds to xbp1 mRNA. Any new genes or mechanisms identified through this approach will be examined for possible effects on retinal degeneration in a Drosophila model for ADRP, where an endogenous mutation in a rhodopsin encoding gene triggers a dominant form of age-related retinal degeneration. As the fly model shows a striking degree of similarity with the human condition, we believe that a successful outcome of this study may directly influence the development of new strategies against ADRP in humans. PUBLIC HEALTH RELEVANCE: Mutations in the rhodopsin gene are responsible for approximately a quarter of autosomal dominant forms of Retinitis Pigmentosa (ADRP), a genetic disease that leads to blindness in individuals 40 ~ 60 years of age. Thus, a better understanding of the mechanisms that help the elimination of misfolded rhodopsins may have a direct impact on developing new therapeutic strategies against this disease.