Combining With Tfam Mitofilin Affect Mitochondrial Dna Transcription

The mitochondrial oxidative phosphorylation (OXPHOS) system is the final biochemical pathway in the production of ATP. Its deficiency plays an important role in various types of human pathologies, such as inherited mitochondrial diseases, age-associated common diseases and ageing. It is well known that the OXPHOS system consists of five multiprotein complexes, the individual subunits of which are encoded either by the mitochondrial or by the nuclear genome. So the regulation of oxidative phosphorylation system is a complex but also fine tuning process. mtDNA transcripts include13subunits which are necessary for respiratory chains, and its regulation may be important in response to different physiological demands.Mitofilin is an inner membrane protein. In order to identify its function, Dr. Lihong-Sun and Dr Ruifeng-Yang firstly established Mitofilin knock-out mice. Starting from E7.5, Mitofilin null embryos were considerably smaller in size than their wild-type or heterozygous littermates. We confirmed the activities of the respiratory chain complexes in Mitofilin heterozygous tissues by enzyme staining, in vitro respiratory chain activity detection, HPLC for ATP supply and mtDNA encoded subunits detection assays. As we know, three subunits of complex Ⅳ are encoded by mtDNA and the others are encoded by nuclear DNA. Distinguished from complex Ⅳ, the subunits of complex Ⅱ are encoded by nuclear gene totally. So, these results suggest that Mitofilin may modulate oxidative phosphorylation by regulating mtDNA transcription.The transcriptional responses caused by lack of Mitofilin prompt us to investigate whether the protein binds to regulatory regions of mtDNA. As expected, through immunoprecipitation and GST pulldown, we found that Mitofilin interacted with mitochondrial transcriptional factors. Its deficiency causes TFAM binding decreased in the mtDNA promoter, which leads to decrease mtDNA transcripts. Based on these results, we propose that Mitofilin may promote the mitochondrial transcriptional factor TFAM close to mtDNA promoter and initiate transcription. In conclusion, Mitofilin modulates mtDNA transcription by affecting transcriptional factor binding in the mtDNA promoter. It may be a machenism for fine tuning oxidative phosphorylation regulation.