ARTICLES & RESEARCH

ARTICLES AND RESEARCH

Dr Harel & Dr Yoon:


ATPase family AAA-domain containing protein 3A (ATAD3A) is a nuclear-encoded mitochondrial membrane-anchored protein involved in diverse processes including mitochondrial dynamics, mitochondrial DNA organization, and cholesterol metabolism. Biallelic deletions (null), recessive missense variants (hypomorph), and heterozygous missense variants or duplications (antimorph) in ATAD3A lead to neurological syndromes in humans.

J Exp Med 2021 10; 218(10):


Mitochondrial DNA (mtDNA) has been suggested to drive immune system activation, but the induction of interferon signaling by mtDNA has not been demonstrated in a Mendelian mitochondrial disease. We initially ascertained two patients, one with a purely neurological phenotype and one with features suggestive of systemic sclerosis in a syndromic context, and found them both to demonstrate enhanced interferon-stimulated gene (ISG) expression in blood. We determined each to harbor a previously described de novo dominant-negative heterozygous mutation in ATAD3A, encoding ATPase family AAA domain-containing protein 3A (ATAD3A). We identified five further patients with mutations in ATAD3A and recorded up-regulated ISG expression and interferon α protein in four of them. Knockdown of ATAD3A in THP-1 cells resulted in increased interferon signaling, mediated by cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING). Enhanced interferon signaling was abrogated in THP-1 cells and patient fibroblasts depleted of mtDNA. Thus, mutations in the mitochondrial membrane protein ATAD3A define a novel type I interferonopathy.


 ATAD3

Dr Yoon:


In 2016, we found that de novo variants (p.Arg528Trp), homozygous ATAD3A missense variants (p.Thr53Ile), and biallelic deletion (two copy deletion) in ATAD3A cause neurological syndrome (Harel, Yoon, et al 2016). ­Clinical findings are varied depending on what kinds of genetic alteration occur. Individuals with p.Arg528Trp displayed developmental delay, hypotonia, peripheral neuropathy, and/or hypertrophic cardiomyopathy and/or optic atrophy. In contrast, individual with large deletion in two copies of ATAD3A gene presented with very severe phenotypes – respiratory failure, brain malformation, and neonatal lethality. Hence, it is critically important to know the genetic mode and effects of ATAD3A variants for diagnosis and patient care.

 Since our initial findings, Dr. Harel and I have sought to identify additional genetic changes in ATAD3A gene. In this study, we report 13 individuals from 8 unrelated families with biallelic ATAD3A variants. Those include 6 single nucleotide variants (SNVs) in trans to deletion alleles. To determine whether the variants identified from individuals play a role in disease, I developed a new Drosophila model that lacks Drosophila Atad3a gene, and instead enable to producing ATAD3A proteins with patient variants. Using this novel system, we found that 4 SNVs severely impair the gene function, and lead to defects in neuronal developments in Drosophila. On the contrary, the other two SNVs are partial loss of ATAD3A function, and cause mitochondrial defects.

Our studies expand allelic spectrum of ATAD3A variants and demonstrate the efficient system in Drosophila for functional interpretation of variants. 


 Recurrent De Novo and Biallelic Variation of ATAD3A, Encoding a Mitochondrial Membrane Protein, Results in Distinct Neurological Syndromes - Lead Authors Dr Harel & Dr Yoon 

 Dr Yoon:

We have been working on genetic mechanisms for diseases  resulted from yet unknown causes. In 2015, we identified a group of patients presenting with global developmental delays, hypotonia, neurological problem (axonal neuropathy). Some patients presented with optic atrophy and cardiom yopathy as well. Whole-exome sequencing (reading all of the protein-coding region of genes in the genome) of patients’ cells revealed de novo mutation (Arginine residue position528 is changed to Tryptophan; p.Arg528Trp) in the gene called ATAD3A, that encodes mitochondrially-localized protein. de novo variants arise in a germ cell (egg or sperm) of one of the parents. We also found that biallelic (both DNA copies) ATAD3A deletion is associated with neonatal lethality. To test whether de novo mutation (p.Arg528Trp) causes pathological consequences, we decided to use fruit flies (Drosophila) because the fruit fly has sophisticated genetic  tools that enable testing human mutations. We introduced ATAD3A carrying Arg528Trp mutation into fruit flies, and found the mutant protein is toxic, and cause abnormal mitochondrial numbers and shapes in neurons and muscles. We also found that skin fibroblast cells from patient who carries de novo p.Arg528Trp mutation, showed problem for mitochondria turnover. Fruit flies completely lacking ATAD3A (similar condition to bialleic ATAD3A deletion) showed early lethality and dramatic reduction of mitochondrial numbers. Collective data showed that de novo and biallelic mutations in ATAD3A cause new human neurological syndrome (now known as Harel-Yoon syndrome), and Drosophila research showed that abnormal mitochondria turnover and shape underlie the syndrome.

Currently, using Drosophila and human iPS cells, I am studying on the mechanisms how mutations in ATAD3A lead to mitochondrial and other cellular problems.

ATPase-d eficient mitochondrial inner membrane protein ATAD3A disturbs mitochondrial dynamics in dominant hereditary spastic paraplegia - Lead Author Dr Henna Tyynismaa

Dr Tyynismaa:

In our study we searched for the genetic cause of spasticity in one family and found it to be a mutation in ATAD3A gene. This family had two affected members, a woman who had lower leg spasticity and her son who had severe spasticity of legs and arms and dyskinetic cerebral palsy. The mutation was located in the ATPase domain of ATAD3A, and we used biochemical methods to demonstrate that the mutation abolished the ATPase activity of ATAD3A. We also studied skin fibroblasts of the older patient and neurons derived from her induced pluripotent stem cells for mitochondrial distribution and dynamics. This study was the first to show that ATAD3A-associated disease can be dominantly inherited, and that it can lead to a variable degree of spastic paraplegia. 

The AAA+ ATPase ATAD3A Controls Mitochondrial Dynamics at the Interface

Dynamic interactions between components of the outer (OM) and inner (IM) membranes control a number of critical mitochondrial functions such as channeling of metabolites and coordinated fission and fusion. We identify here the mitochondrial AAA+ ATPase protein ATAD3A specific to multicellular eukaryotes as a participant in these interactions. The N-terminal domain interacts with the OM. A central transmembrane segment (TMS) anchors the protein in the IM and positions the C-terminal AAA+ ATPase domain in the matrix. Invalidation studies in Drosophila and in a human steroidogenic cell line showed that ATAD3A is required for normal cell growth and cholesterol channeling at contact sites. Using dominant-negative mutants, including a defective ATP-binding mutant and a truncated 50-amino-acid N-terminus mutant, we showed that ATAD3A regulates dynamic interactions between the mitochondrial OM and IM sensed by the cell fission machinery. The capacity of ATAD3A to impact essential mitochondrial functions and organization suggests that it possesses unique properties in regulating mitochondrial dynamics and cellular functions in multicellular organisms.


OTHER DISEASES LINKED WITH GENE ATAD3A  DISFONCTION

ATAD3A oligomerization causes neurodegeneration by coupling mitochondrial fragmentation and bioenergetics defects - Lead Author Dr Xin Qi

Mitochondrial fragmentation and bioenergetic failure manifest in Huntington’s disease (HD), a fatal neurodegenerative disease. 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 HD. 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 cells. 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, suggesting that DA1 might be useful for developing HD therapeutics.

Mitochondrial ATAD3A combines with GRP78 to regulate the WASF3
metastasis-promoting protein -  Lead Author Dr Yong Teng

The ATPase family AAA-domain containing protein 3A (ATAD3A), a nuclear-encoded mitochondrial enzyme, is involved in diverse cellular processes, including mitochondrial dynamics, cell death and cholesterol metabolism. Overexpression and/or mutation of the ATAD3A gene have been observed in different types of cancer, associated with cancer development and progression. The dysregulated ATAD3A acts as a broker of a mitochondria-endoplasmic reticulum connection in cancer cells, and inhibition of this enzyme leads to tumor repression and enhanced sensitivity to chemotherapy and radiation. As such, ATAD3A is a promising drug target in cancer treatment.

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