Adenylosuccinate Synthetase Deficiency Results in Neuromuscular Defects in Caenorhabditis elegans

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Author:
Jin, Melinda
Area of Honors:
Biochemistry and Molecular Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Wendy Hanna-Rose, Thesis Supervisor
Ying Gu, Thesis Honors Advisor
Keywords:
C. elegans
Adenylosuccinate Synthetase
ADSS1 Myopathy
Purine Metabolism
Abstract:
ADSS1 myopathy is a rare neuromuscular disorder caused by mutation in the ADSS1 gene, which encodes for an enzyme involved in purine biosynthesis, adenylosuccinate synthetase or ADSS. Patients with ADSS1 myopathy exhibit progressive muscle weakness and atrophy beginning in childhood. As a recently recognized disease in 2016, ADSS1 myopathy has been poorly characterized and has no standard treatment. Many patients go undiagnosed or misdiagnosed due to the disease’s low prevalence and its similarity to other disorders. Pre-clinical animal models have significant potential to increase our understanding of the mechanisms of ADSS1 myopathy. The Hanna-Rose Lab utilizes the nematode Caenorhabditis elegans as a model for purine metabolism disorders. Previously, our lab established that adss-1 reduction-of-function animals exhibit a variety of mobility and neuromuscular phenotypes, including reduced speed, uncoordinated movement, and impaired postsynaptic cholinergic signaling. This suggests that ADSS is important for normal neuromuscular function. My research expands on this hypothesis and focuses on characterizing an adss-1 loss-of-function model to further investigate the functions of ADSS. I first examined if ADSS plays a role in development and have found that deletion of adss-1 results in developmental delay, small size, and reproductive system defects. To identify if adss-1 loss-of-function animals also have mobility defects, I used WormLab® software to analyze movement. I determined that the adss-1 loss-of-function mutant animals have reduced speed and altered swimming coordination more severe than adss-1 reduction-of-function animals. Additionally, I examined sensory phenotypes and found that deletion of adss-1 causes impairments to touch response and tap reflex response, but it does not affect osmosensation. I also identified organizational defects in the mitochondria of body wall muscle in adss-1 mutant animals. These experiments indicate that ADSS is required for normal development, movement, mechanosensation, and mitochondrial organization. Finally, I hypothesized that inhibition of purine degradation may rescue the previous phenotypes observed in adss-1 loss-of-function animals. I used both knockdown of xdh-1 and supplementation of febuxostat (FBX) and adenine to target xanthine dehydrogenase (XDH), an enzyme involved in purine catabolism. I found that knockdown of xdh-1 partially rescues size and movement phenotypes in adss-1 mutant animals. However, supplementation of FBX and adenine shows no effect on size nor mobility phenotypes. I found that FBX and adenine may have a mild restorative effect on nose touch response but not plate touch response. Supplementation of FBX and adenine shows the most potential in rescuing mitochondrial fragmentation in body wall muscle of adss-1 mutant animals. These experiments suggest that XDH may be a useful therapeutic target for treating symptoms of ADSS deficiency. My research provides a greater understanding of the biological role of ADSS and the mechanisms of ADSS1 myopathy using a C. elegans adss-1 loss-of-function model. I identified a variety of phenotypes associated with deletion of adss-1 and tested a potential therapeutic target for treating adss-1 defects. Improving our knowledge of ADSS and ADSS1 myopathy is important for the development of treatment options for this understudied disease.