Reticulon3Attenuates The Clearance Of Cytosolic Prion Aggregates Via Inhibiting Autophagy

Prion diseases are protein virus which could cause neurodegenerative diseases of human and animals. The causative agent of prion diseases is a protein factor-PrPSc, which could transform the normal PrPC into pathogenic PrPSc, resulting in the lesions and degeneration of nerive tissue. Prion diseases include scrapie, Gerstmann Straussler Scheinker disease (GSS), Kuru, fatal familial insomnia (FFI), Creutzfeldt-Jakob disease (CJD).Autophagy is an inducible lysosomal-dependent intracellular degradation pathway, which is important for the equilibrium of the intracellular environment of the cell. Under background level, nutritional deficiency or environmental stress conditions, double-membrane vesicles called autophagosomes will engulf part of cytosol and organelle, deliver them to lysosome for degradation, followed by releasing nutrients into cytosol for necessary material and energy of metabolism. It has reported that autophagy plays an important role in neurodegenerative diseases and could protect against neurodegeneration. Inhibition of mTOR induces autophagy to reduce the toxicity of polyglutamine expansion in fly and mouse models of Huntington’s disease in vivo. Autophagy is activated and is abnormal in the AD mouse model of amyloidosis. Autophagic vacuoles have also been reported in neurons in experimental animal models of prion disease and Gerstmann-Straussler-Scheinker (GSS) syndrome. Despite the importance of the autophagy pathway in cell survival, the function of autophagy in prion disease remains unclear.Reticulon3(RTN3) belongs to the reticulon family which is widely expressed in human tissues with the highest expression in the brain and is predominantly localized at endoplasmic reticulum. RTN3has recently been identified as a negative modulator of BACE1and transgenic mice overexpressing RTN3develops neuritic abnormalities similar to those observed in Alzheimer’s disease (AD) brains. These data suggest that RTN3plays an important role in neurodegenerative diseases, although its’mechanism remains unclear. Previous works include an increase in the [Ca2+] of the cytoplasm triggers autophagy, the regulation of ER Ca2+by RTN3, the interaction between RTN3and Bcl-2and the inhibition of autophagy by the binding of Bcl-2to Beclinl, suggesting that RTN3may regulates autophagy under ER stress.Based on the existing findings that disease-associated prion proteins could activate ER stress and autophagy, ER stress induced autophagy and, possibly, RTN3-regulated autophagy, we raised a testable hypothesis that prion protein aggregates activate ER stress, then RTN3is induced to participate in the regulation of autophagy to control the clearance of aggregates.In this study, we used human cyPrP (PrP90-231) expressing in the cytoplasm to stimulate the characteristics of scrapie conformation PrPSc. CyPrP aggregates caused ER stress, the activation of RTN3, induction of autophagy, the impairment of UPS and apoptosis. Knocking down RTN3enhanced the induction of autophagy, the negative regulation of RTN3to autophagy is via the enhanced binding between Bcl-2and Beclinl promoted by RTN3, which enhances Bcl-2-mediated inhibition of Beclinl-dependent autophagy. Subsequently cyPrP aggregates were cleared to resume the activity of the UPS and alleviate ER stress. This process ultimately inhibited cell death and maintained cellular homeostasis. To the best of our knowledge, this is the first study to report that RTN3negatively regulates autophagy to block the clearance of cyPrP aggregates and provide a clue regarding the potential to induce autophagy for the treatment of prion disease and other neurodegenerative diseases such as PD, AD and HD.