Tissue specific effects of NAD+ biosynthesis on muscle function, fat metabolism and gonad development in Caenorhabditis elegans

Open Access
Author:
Wang, Wenqing
Graduate Program:
Biochemistry, Microbiology, and Molecular Biology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
October 02, 2014
Committee Members:
  • Wendy Hanna Rose, Committee Chair
  • Melissa Rolls, Committee Member
  • Lorraine C Santy, Committee Member
  • Scott Brian Selleck, Committee Member
  • Ramesh Ramachandran, Committee Member
Keywords:
  • NAD+
  • vitamin B3
  • nicotinamidase
  • nicotinamide riboside
  • quinolinic acid
  • metabolomics
  • glucose metabolism
  • lipid metabolism
Abstract:
Both acting as a cofactor in diverse biochemical reactions, and as an obligate co-substrate for NAD+ consumers which regulate a number of key cellular processes, nicotinamide adenine dinucleotide (NAD+) is a critical molecule in cellular metabolism. Our lab has established an excellent C. elegans model system to study the developmental roles of NAD+ biosynthesis. Mutation in the C. elegans nicotinamidase PNC-1, the first enzyme in NAD+ salvage biosynthesis from nicotinamide (NAM) causes a spectrum of developmental defects, which are separately related to the PNC-1 biological function of NAM clearance or NAD+ production. In my study, I investigated the tissue specific defects on muscle functions, fat metabolism and gonad development caused by defective NAD+ biosynthesis. Because the live bacterial diet provides NAD+ precursors and possibility NAD+ to support C. elegans growth, the NAD+ biosynthesis defective pnc-1 mutants are more susceptible to dietary changes, and low quality diet induces abnormal fat accumulation and exacerbates gonad developmental delay in pnc-1 mutants. I used a metabolomics approach to gain a comprehensive understanding of the effect of defective NAD+ biosynthesis on global metabolism. Although blocking NAD+ salvage from NAM only moderately depletes NAD+ in pnc-1 mutants, it leaves a broad impact on metabolism. Metabolomics data have shown that glycolysis is defective in pnc-1 mutants, which as works of my colleagues pointed out, may be an underlying cause of pnc-1 gonad developmental defects. Besides NAD+ salvage biosynthesis from NAM, salvage from nicotinamide riboside (NR) and de novo NAD+ biosynthesis from tryptophan also contribute to building the NAD+ reservoir in C. elegans. Interestingly, a key enzyme in the de novo NAD+ synthesis pathway is absent from C. elegans genome, nonetheless, metabolites in de novo pathway functions as NAD+ precursors in promoting gonad development. Although endogenous NR salvage and de novo NAD+ biosynthesis are not the major NAD+ source in C. elegans, their activities are important for body wall muscle functions when NAM salvage is compromised. In summary, my work has expanded our knowledge of how NAD+ biosynthesis regulates physiological processes via modulation of NAM and NAD+ levels. I have demonstrated the tissue specific contributions made by different NAD+ biosynthesis pathways. The established metabolomics profile of pnc-1 mutants provides insights into its influence on global metabolism, and my work will help to decipher how metabolic perturbations lead to developmental and physiological consequences.