Abstract：
Endoplasmic reticulum (ER) Ca2+ homeostasis relies on an appropriate balance between efflux- and influx-channel activity responding to dynamic changes of intracellular Ca2+ levels. Dysregulation of this complex signaling network has been shown to contribute to neuronal and photoreceptor death in neuro- and retinal degenerative diseases, respectively. In mice with cone cyclic nucleotide-gated (CNG) channel deficiency, a model of achromatopsia/cone dystrophy, cones display early-onset ER stress-associated apoptosis and protein mislocalization. Cones in these mice also show reduced cytosolic Ca2+ level and subsequent elevation in the ER Ca2+ -efflux-channel activity, specifically the inositol-1,4,5-trisphosphate receptor type 1 (IP3 R1), and deletion of IP3 R1 results in preservation of cones. This work investigated how preservation of ER Ca2+ stores leads to cone protection. We examined the effects of cone specific deletion of IP3 R1 on ER stress responses/cone death, protein localization, and ER proteostasis/ER-associated degradation. We demonstrated that deletion of IP3 R1 improves trafficking of cone-specific proteins M-/S-opsin and phosphodiesterase 6C to cone outer segments and reduces localization to cone inner segments. Consistent with the improved protein localization, deletion of IP3 R1 results in increased ER retrotranslocation protein expression, reduced proteasome subunit expression, reduced ER stress/cone death, and reduced retinal remodeling. We also observed the enhanced ER retrotranslocation in mice that have been treated with a chemical chaperone, supporting the connection between improved ER retrotranslocation/proteostasis and alleviation of ER stress. Findings from this work demonstrate the importance of ER Ca2+ stores in ER proteostasis and protein trafficking/localization in photoreceptors, strengthen the link between dysregulation of ER Ca2+ homeostasis and ER stress/cone degeneration, and support an involvement of improved ER proteostasis in ER Ca2+ preservation-induced cone protection; thereby identifying IP3 R1 as a critical mediator of ER stress and protein mislocalization and as a potential target to preserve cones in CNG channel deficiency.
摘要：
内质网（ER）Ca2稳态依赖于响应细胞内Ca2水平动态变化的流出和内流通道活性之间的适当平衡。这种复杂的信号网络的失调已被证明有助于神经和视网膜退行性疾病中的神经元和光感受器死亡。分别。在患有视锥环核苷酸门控（CNG）通道缺陷的小鼠中，色盲/视锥细胞营养不良的模型，视锥细胞显示早发性内质网应激相关的细胞凋亡和蛋白质错位。这些小鼠的锥体还显示出细胞溶质Ca2+水平降低和随后的ERCa2+流出通道活性升高，特别是肌醇1,4,5-三磷酸受体1型（IP3R1），和IP3R1的缺失导致视锥的保存。这项工作调查了ERCa2+储存的保存如何导致锥体保护。我们检查了视锥特异性缺失IP3R1对ER应激反应/视锥死亡的影响，蛋白质定位，和ER蛋白停滞/ER相关降解。我们证明，IP3R1的缺失可改善视锥细胞特异性蛋白M-/S-视蛋白和磷酸二酯酶6C向视锥细胞外段的运输，并减少视锥细胞内段的定位。与改进的蛋白质定位一致，IP3R1缺失导致ER反转录蛋白表达增加，蛋白酶体亚基表达减少，减少ER压力/锥体死亡，减少视网膜重塑.我们还观察到用化学伴侣治疗的小鼠内质网逆行移位增强，支持改善内质网逆行转位/蛋白抑制和缓解内质网应激之间的联系。这项工作的结果证明了ERCa2存储在ER蛋白停滞和光感受器中的蛋白质运输/定位中的重要性，加强ERCa2+稳态失调与ER应激/视锥退化之间的联系，并支持改善的ER蛋白抑制参与ERCa2保留诱导的视锥保护；从而将IP3R1鉴定为ER应激和蛋白质错误定位的关键介质，并作为在CNG通道缺陷中保留视锥的潜在靶标。
