Mitochondrial PARP1 Regulates NAD+-dependent Poly ADP-ribosylation on Mitochondrial Nucleoids

Poly ADP-ribose (PAR) polymerases (PARPs) play fundamental roles in multiple DNA damage recognition and repair pathways. Persistent nuclear PARP activation causes cellular NAD+ depletion and exacerbates cellular aging. However, very little is known about mitochondrial PARP (mtPARP) and PARylation. The existence of mtPARP is controversial, and the biological roles for mtPARP induced mitochondrial PARylation are unclear. Here, we demonstrate the presence of PARP1 and PARylation in purified mitochondria. The addition of the PARP1 substrate NAD+ to isolated mitochondria induces PARylation which is suppressed by PARP inhibitor olaparib treatment. Mitochondrial PARylation was also evaluated by enzymatic labeling of terminal ADP-ribose (ELTA) labeling. To further confirm the presence of mtPARP1, we evaluated mitochondrial nucleoid PARylation by ADP ribose-chromatin affinity purification (ADPr-ChAP) . We observed that NAD+ stimulated PARylation and TFAM occupancy on the mtDNA regulatory region D-loop, inducing mtDNA transcription. These findings suggest that PARP1 is integrally involved in mitochondrial PARylation and NAD+ dependent mtPARP1 activity contributes to mtDNA transcription regulation. Overall design: TFAM ChIP or ADPr-ChAP were performed with isolated mitochondria from HeLa cells that are treated with DMSO (control), NAD+, NAD+ with olaparib.