CERKL Regulates Autophagy Via The NAD Dependent Deacetylase SIRT1

Autophagy is a self-degrading pathway that plays an important role in maintaining cell homeostasis.Disorders of autophagy can lead to diseases such as cancer,immune diseases,and neurodegenerative diseases.Autophagy in the retina plays an important role in maintaining the homeostasis of photoreceptor cells and RPE.Autophagy in RPE participates in the phagocytic function of RPE through a non-canonical pathway,and maintains the visual function of photoreceptor cells by degrading the outer segment of photoreceptor cells and recycling the substances therein.Retinitis pigmentosa is a kind of hereditary neurodegenerative disease and one of the main causes of hereditary blindness.CERKL is a retinal degeneration disease gene cloned in 2004.Here,we use cerkl knockout zebrafish,combined with cell experiments to continue to study and explore the physiological mechanism of CERKL mutation leading to retinitis pigmentosa and the molecular function of CERKL.In vitro and in vivo experiments have shown that inhibition or knockout of CERKL expression leads to a decrease in autophagy levels in cells,suggesting that impaired autophagy may be an important cause of photoreceptor cell degeneration in cerkl knockout zebrafish.The study found that CERKL regulates autophagy via SIRT1.SIRT1 is one of the main regulators of acetylation/ deacetylation in autophagy.SIRT1 was down-regulated in CERKL-depleted cells and cerkl knockout zebrafish.SIRT1,was down-regulated in CERKL-depleted cells and cerkl knockout zebrafish.Moreover,the levels of acetylation of ATG5 and ATG7 are upregulated in CERKL-depleted cells.This indicates that CERKL regulates autophagy via SIRT1.At the same time,overexpression of SIRT1 can recover the level of autophagy that downregulated in CERKL-depleted cells,whereas in in SIRT1-depleted cells,CERKL loses its ability to regulate autophagy.This suggests that the ability of CERKL to regulate autophagy depends on SIRT1.Further research indicates that CERKL regulates SIRT1 at the protein level.We found that the half-life of SIRT1 was significantly shortened after knocking down CERKL,while the protein stability of SIRT1 was increased after overexpression of CERKL.This indicates that CERKL is able to regulate the protein stability of SIRT1.The stability of SIRT1 is regulated by phosphorylation of Ser27 and Ser47.We found that CERKL regulates the phosphorylation of the two sites and regulates the protein stability of SIRT1 by regulating the phosphorylation of SIRT1.We found that there is an interaction between CERKL and SIRT1 and the phosphorylation at SIRT1 Ser27 affects the interaction between SIRT1 and CERKL.Taken together,we found that CERKL plays a critical role in regulating autophagy by stabilizing SIRT1.In cerkl knockout zebrafish,deletion of Cerkl results in the degradation of Sirt1,which suppresses autophagy,and eventually leads to degeneration of photoreceptor cells.