Peroxisome Proliferator-activated Receptor Co-activator 1 (PGC-1 ) and Sirtuin 1 (SIRT1) Reside in Mitochondria POSSIBLE DIRECT FUNCTION IN MITOCHONDRIAL BIOGENESIS*□

The transcriptional co-activator PGC-1 and the NAD -dependent deacetylase SIRT1 are considered important inducers of mitochondrial biogenesis because in the nucleus they regulate transcription of nucleus-encodedmitochondrial genes. We demonstrate that PGC-1 and SIRT1 are also present inside mitochondria and are in close proximity tomtDNA. They interact with mitochondrial transcription factor A (TFAM) as assessed by confocal microscopy analysis and by blue nativePAGE. Nucleoid purification allowed us to identify SIRT1 and PGC-1 as proteins associated with native and cross-linked nucleoids, respectively. After mtDNA immunoprecipitation analysis, carried out on mitochondrial extracts, we found that PGC-1 is present on the same D-loop region recognized by TFAM. Finally, by oligonucleotide pulldown assay, we found PGC-1 and SIRT1 associated with the TFAM consensus sequence (human mitochondrial transcription factor-binding site H). The results obtained suggest that in mitochondria PGC-1 and SIRT1 may function as their nuclear counterparts and represent the genuine factors mediating the cross-talk between nuclear and mitochondrial genome. Finally, this work adds new knowledge on the function of SIRT1 and PGC-1 and highlights the direct involvement of such proteins in regulation of mitochondrial biogenesis.