The Mechanism Of Desmosterol Induced Resistance To Ferroptosis In Tumor Cells

Ferroptosis,as an emerging form of cell death,is mainly driven by iron-dependent lipid peroxidation.Ferroptosis plays an important role in the occurrence and development of tumors,neurodegenerative diseases,ischemia-reperfusion injury and other related diseases.Therefore,targeting ferroptosis as vulnerability may provide novel therapeutic strategies for such diseases.As an important component of animal cell plasma membrane,cholesterol is necessary for maintaining membrane integrity and organization,and plays an important role in lipid metabolism.Cholesterol is ubiquitous in the plasma membrane of eukaryotic cells and inherently sensitive to oxidants such as hydroxyl radicals.In a screen for cholesterol metabolites as potential ferroptosis modulators our laboratory has discovered that several cholesterol precursors,7-dehydrocholesterol(7-DHC)and desmosterol are effective ferroptosis inhibitors,inhibits 7-DHC,which has a higher redox activity than cholesterol,has been reported to suppress ferroptosis.In a previous work,we have characterized the functions of cholesterol in ferroptosis.Here we focus on desmosterol,for its detailed mechanism of action in preventing ferroptosis.We first tested the effect of desmosterol in tumor cells under various conditions:RLS3,Erastin,GPX4 knockout or cystine starvation.It was found that desmosterol could block ferroptosis in all conditions,flow cytometry and fluorescence inhibition autooxidation(FENIX)detection showed that desmosterol did not act as an antioxidant to reduce the levels of lipid peroxidation during the occurrence of ferroptosis,as well as not affect the expression of ferroptosis related proteins.Through a series of genetic and pharmacological methods we found that desmosterol inhibited ferroptosis partly through the ferroptosis inhibitor protein 1(FSP1)CoQ10 axis by increasing the content of CoQ10 in tumor cells.Further investigation of the effect of desmosterol on the key proteins in sterol biosynthesis pathway found that SQLE protein was degraded by desmosterol,and SQLE knockout cells were also resistant to ferroptosis.Previous studies have shown that reduction of SQLE protein led to an increase in the content of squalene,a natural antioxidant that protects cells from damaging free radicals by reducing lipid peroxidation.Combined blockade of CoQ10 and squalene synthesis completely abolished the inhibitory effect of desmosterol on ferroptosis,indicating that desmosterol confers cell resistance to ferroptosis by increasing the content of both CoQ10 and squalene.Animal studies have also demonstrated that desmosterol can prevent ferroptosis and reduce lipid peroxidation levels in tumor cellsTherefore,by inducing SQLE degradation,desmosterol may,on the one hand,lead to the accumulation of squalene,thereby reducing lipid peroxidation to inhibit ferroptosis,on the other hand,it also results in increased CoQ 10 content in the non-sterol branch,thus contributes to ferroptosis inhibition in tumor cells through the FSP1-CoQ10 pathway.Taken together,in this study,we have explored the molecular mechanism by which desmosterol acts as a new ferroptosis inhibitor.Our work may pave a way to the discovery of a new target for tumor therapy.