Using Drosophila Melanogaster To Study The Pathogenesis Of Retinitis Pigmentos

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 threedimensional 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,IRE 1,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,RhoP23H,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 IRE 1,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,ninaEG69D.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.