The Functional Role Of A Novel Beclin1 Splicing Variant—Beclin1 V In Mitophagy Regulation

It is well known that mitochondria are a cell’s energy factories, it can contribute to cell survival by surpplying enough energy and metabolic intermediate via aerobic respiration, whereas this procession also can produce by-products such as ROS, and abnormal ROS accumulation will cause mitochondrial damage, leading to the release of apoptosis associated protein such as cytochrome C.further activating downstream Caspase and promoting apoptosis. So in order to maintain cell homeostasis, these damaged mitochondria should be removed in time. Those damaged mitochondria can be selectively eliminated by autophagy pathway.which is so called mitophagy. And studies have also shown that in some important physiological processes, mitophagy plays an important role, for example, during maturation of red blood cells from reticulocyte, mitochondria that are no longer needed will be cleared by mitophagy. In addition an increasing number of studies found that mitophagy is closely related to neurodegenerative diseases, such as Parkinson’s disease, mutation of the two genes encoding Parkin and Pinkl protein happens frequently in this disease, thus leading to mitophagy defects.The mechanism about mitophagy has not yet been clarified clearly until now. So far there mainly are three pathways that participate in regulation of mammalian mitophagy.(1) Mitophagy depending on Pink1/Parkin pathway(2) Mitophagy relying on NIX during maturation of red blood cells from reticulocyte(3) Mitophagy mediated by FUNDC1 under hypoxiaTherefore we need more research to profoundly understand the specific mechanism on selective degradation of mitochondria.And our work has discovered a new splicing mutant of the autophagy related protein Beclinl for the first time and named it Beclinl v. Exon 9,10,11 of Beclinl,encoding 70 amino acids,have been missed in Beclinl v compared with Beclin1,while exon 8 and 12 are connected directly. Becnl v exists in different cell lines, mainly located in the outer membrane of mitochondria. Becnl v is not required for non-specific autophagy due to starvation, which is greatly different from Becnl.however, overexpression of Beclinlv in several cell lines can induce mitochondria aggregation and further mitochondria loss,which can be inhibited by Lysosomal inhibitor Baf.A. But Beclinl does not affect mitochondria any more.And we also found that knockdown of endogenous Becnl v could remarkably inhibit mitophagy induced by starvation or CCCP, whereas Beclinl had no obvious influence on the process.So above all,our results have demonstrated Beclinl v is specifically involved in mitophagy regulation,whereas Beclinl function mainly in non-specific autophagy.For the specific mitochondrial localization of Beclinl v, we supposed that it may serve as an adaptor protein involved in mitophagy regulation, which is similar to those previously reported adaptor protein participating in mammalian cell mitophagy.until now we have found that Beclinl v does not induce mitophagy through directly interaction with LC3 UBL family protein via its typical LC3 interaction region (LIR)-W/YXXL/I. Furthermore mitophagy induced by Beclin1 v is also not dependent on p62, so what is the exact mechanism of mitophagy caused by Beclinl v? Why Beclinlv is specifically located to mitochondria when missing the three exons 9,10,11, compared to Beclinl? These problems are still a mystery to us and we need further experiments to find out the answers.