ATAD3A oligomerization causes neurodegeneration by coupling mitochondrial fragmentation and bioenergetics defects Xin Qi1,2*, Yuanyuan Zhao1, Xiaoyan Sun1, Domenick A. Prosdocimo3,4, Mukesh K. Jain3,4, Charles Hoppel2,5 and Rajesh Ramachandran1 1Department of Physiology & Biophysics, 2Center for Mitochondrial Disease, 3Case Cardiovascular Research Institute and Harrington Heart & Vascular Institute, 4Department of Medicine, University Hospitals Case Medical Center, 5Department of Pharmacology, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA *Corresponding author: Xin Qi PhD, Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave, E516, Cleveland, Ohio, 44106-4970, USA. Tel: 216-368-4459; e-mail: firstname.lastname@example.org Mitochondrial fragmentation and bioenergetic failure manifest in many neurodegenerative diseases. The factors that couple mitochondrial fusion/fission with bioenergetics and their impacts on neurodegeneration however remain poorly understood. Our proteomic analysis identifies mitochondrial protein ATAD3A as an interactor of mitochondrial fission GTPase, Drp1, in Huntington's disease (HD), a fatal neurodegenerative disease. Here we show that, in HD, ATAD3A dimerization due to deacetylation at K135 residue is required for Drp1-mediated mitochondrial fragmentation. Disturbance of ATAD3A steady state impairs mtDNA maintenance by disrupting TFAM/mtDNA binding. Blocking Drp1/ATAD3A interaction with a peptide, DA1, abolishes ATAD3A oligomerization, suppresses mitochondrial fragmentation and mtDNA lesion, and reduces bioenergetic deficits and cell death in HD mouse- and patient-derived neurons. DA1 treatment reduces behavioral and neuropathological phenotypes in HD transgenic mice. Our findings demonstrate that ATAD3A plays a key role in neurodegeneration by linking Drp1-induced mitochondrial fragmentation to defective mtDNA maintenance, and suggest that DA1 might be useful for developing therapeutics for HD or other neurodegenerative diseases in which ATAD3A is aberrantly activated.