在膜蛋白的合成和成熟过程中，内质网的质量监控体系发挥着至关重要的作用。内质网中的分子伴侣以及折叠催化酶会辅助蛋白形成正确的三维结构，只有正确折叠的蛋白会被运送到高尔基体进行进一步的加工折叠并最终成熟并发挥生理功能。基因突变、翻译错误或者细胞受到较大的外界压力时，会导致内质网上蛋白错误折叠的发生。如这些错误折叠的蛋白不能被及时清除，就会引起内质网应激。内质网应激时，细胞会通过定位在内质网膜上的三个内质网应激感应蛋白PERK、IRE1和ATF6激活未折叠蛋白反应。未折叠蛋白反应下游的转录因子会上调相关基因的表达以减少错误折叠蛋白的合成，降解错误折叠的蛋白，从而缓解内质网压力。如果内质网承受的压力过大，则会引起细胞凋亡来保护机体的其他细胞不受影响。

长时期的内质网应激是许多重要神经退行性疾病的病理特征，包括色素性视网膜炎、阿尔茨海默综合征、帕金森综合征、亨廷顿舞蹈症、肌萎缩性脊髓侧索硬化症等。这些疾病都会在细胞内或细胞间形成错误折叠蛋白的聚集体，影响细胞稳态，导致细胞功能障碍，最终在机体上表现为临床学症状。在突变型视紫红质Rho^P23H引发的常染色体显性色素性视网膜炎中，错误折叠的突变型视紫红质积累在内质网中，引发内质网应激并且破坏感光细胞的蛋白质稳态。感光细胞通过未折叠蛋白反应降解错误折叠的视紫红质来缓解内质网应激压力，但同时导致正常视紫红质的降解而产生负影响。因此，揭示未折叠蛋白反应不同分支对不同形式视紫红质的降解偏向，对于色素性视网膜炎致病机理以及治疗策略的探索至关重要。

本课题创建了以双荧光标记突变型和野生型视紫红质的显性色素性视网膜炎果蝇模型，并深入研究了错误折叠的突变型视紫红质影响野生型视紫红质的分子生物学机制。主要的研究成果有以下三点：

1)PERK信号通路在维持内质网的蛋白质稳态时发挥着核心作用。PERK信号通路的相关基因发生突变会导致内质网中蛋白质稳态失衡，加速野生型视紫红质的降解并使错误折叠的蛋白进一步累积，最终导致细胞死亡。

2)在长期内质网应激中，PERK通过抑制IRE1导致的细胞自噬来保护野生型视紫红质不受错误折叠视紫红质的影响。perk基因突变会导致IRE1过度活化，引发内质网自噬，并通过内质网自噬降解野生型视紫红质。

3)过表达PERK对内源突变导致的色素性视网膜炎果蝇模型ninaE^G69D有明显的保护作用。

本课题研究发现未折叠蛋白反应不同的信号通路在维持内质网稳态过程中发挥着不同的功能；未折叠蛋白反应通过IRE1通路激活内质网自噬，并选择性降解野生型视紫红质；PERK通路上调可以抑制IRE1活性及下游的内质网自噬，在色素性视网膜炎中发挥重要保护作用。本研究不但揭示了内质网应激对内质网自噬的调控机制以及在显性色素性视网膜炎中调控细胞稳态的关键作用等基础问题，并且为色素性视网膜炎等内质网应激相关疾病致病机理的研究和全新靶向药物的开发提供了有价值的信息。

The quality control system of the endoplasmic reticulum (ER) plays a crucial role in the synthesis and maturation of membrane proteins. With the help of molecular chaperones and folding enzymes resident in the ER, the membrane proteins can form proper three-dimensional structures, and only precisely folded proteins are transported to the Golgi apparatus for further processing and folding, and finally mature and perform physiological functions. Proteins misfolding occurs upon genetic mutations, incorrect translation, or when cell is subjected to greater environmental stress. If these misfolded proteins fail to be cleaned up promptly, they will cause ER stress. During ER stress, the unfolded protein response (UPR) will be induced through three ER stress-sensing proteins——PERK, IRE1, and ATF6, which localized on the ER membrane. Transcription factors downstream of UPR will upregulate the expression of related genes to reduce the synthesis of misfolded proteins, degrade misfolded proteins, and relieve ER stress. If the ER stress cannot be mitigated, apoptosis will occur to protect other cells in the body from being affected.

The chronic ER stress is associated with the major neurodegenerative diseases, including autosomal dominant retinitis pigmentosa, Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis etc. In these diseases, aggregates of misfolded proteins form in cells or between cells, which affect intracellular homeostasis, lead to cellular dysfunction and finally manifest clinical symptoms in the body. In the autosomal dominant retinitis pigmentosa (adRP) caused by misfolded rhodopsin, Rho^P23H, mutated rhodopsin accumulated in the ER, triggering ER stress and disrupting protein homeostasis of photoreceptor cells. Photoreceptor cells degrade misfolded rhodopsin through UPR, which alleviates ER stress, but at the same time leads to the degradation of normal rhodopsin, which has a negative effect. Therefore, a comprehensive understanding of the regulation and pathological roles of individual UPR branches in adRP, and mechanisms by which wild-type rhodopsin was degraded are crucial to explore the pathogenesis and treatment strategies of adRP.

In this study, we established a double fluorescence labeling system of adRP Drosophila model, and investigated the molecular biological mechanisms of how misfolded rhodopsin affects wild-type rhodopsin. The main research results are as follows:

1) The PERK signaling pathway plays a central role in maintaining rhodopsin homeostasis in adRP. Mutations in genes related to the PERK signaling pathway interrupt protein homeostasis in ER, accelerate the degradation of wild-type rhodopsin and further accumulate misfolded rhodopsin, ultimately lead to cell death.

2) Upon chronic ER stress, PERK prevents degradation of wild-type rhodopsin by inhibiting IRE1 induced ER-phagy. Mutations in perk lead to excessive activation of IRE1, which degrades wild-type rhodopsin through ER-phagy.

3) Overexpression of PERK protects the photoreceptor cells from degeneration in an endogenous fly model of adRP, ninaE^G69D.

Our study points out that each UPR pathway plays different roles in maintaining ER protein homeostasis; chronic UPR activates ER-phagy through IRE1 pathway, which selectively degrades wild-type rhodopsin; upregulation of PERK pathway inhibits IRE1 activity and downstream ER-phagy, playing a key protective role in adRP. This study not only reveals the fundamental mechanisms of induction of ER-phagy by ER stress, and the key role of ER stress in regulating protein homeostasis in adRP, but also provides insight on the pathogenesis of ER-stress associated diseases such as adRP, and suggests the strategy to treat the disease.