Investigating the Functional Consequences of the DNMT3A Variants Identified in ALS

Abstract

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disease that affects the motor system resulting in paralysis and death. Over the past 10 years, advances in genomic technologies have substantially improved our understanding of the genetic etiology of the disease. Recent exome sequencing studies have indicated an interesting association between DNA methyltransferase 3A (DNMT3A) and ALS. It has also been previously reported that deletion of Dnmt3a in mouse nervous system led to defects in motor function and the neuromuscular system, suggesting an important role of Dnmt3a in motor function development and maintenance. Therefore, I hypothesized that variants in DNMT3A may be associated with increased susceptibility to ALS. Since the DNMT3A variants were all found heterozygous in ALS, they could act via a gain-of-function mechanism or haploinsufficiency. I examined the gain-of-function hypothesis using in vitro cell models and found that many of the ALS-unique variants had increased affinity to heat shock proteins and induced alterations in protein homeostasis, which resembled a converging mechanism in neurodegeneration. I then examined the haploinsufficiency hypothesis using an in vivo mouse model and found that the haploinsufficiency of Dnmt3a did not lead to defects in the neuromuscular system in mice. I also showed that the motor neuron-specific deletion of Dnmt3a did not result in impaired motor functions or neuromuscular system, suggesting that Dnmt3a may support motor function in a motor neuron non-autonomous manner. Together my findings indicated a gain-of-function mechanism for the DNMT3A variants to contribute to the predisposition for ALS by perturbing protein homeostasis, and endorsed the postulation that the proteostasis network may be the underlying common venue for different ALS-causing factors to act in. Furthermore, the link that I established between DNMT3A and ALS would provide a new entry point for therapeutic interventions for the disease.