Nicotinamidase modulation of NAD+ biosynthesis and nicotinamide levels separately affect reproductive development and cell survival inC. elegans

Abstract

Nicotinamide adenine dinucleotide (NAD+) is a central molecule in cellular metabolism and an obligate co-substrate for NAD+-consuming enzymes, which regulate key biological processes such as longevity and stress responses. Although NAD+ biosynthesis has been intensely studied, little analysis has been done in developmental models. We have uncovered novel developmental roles for a nicotinamidase(PNC), the first enzyme in the NAD+ salvage pathway of invertebrates. Mutations in the Caenorhabditis elegans nicotinamidase PNC-1 cause developmental and functional defects in the reproductive system;the development of the gonad is delayed, four uterine cells die by necrosis and the mutant animals are egg-laying defective. The temporal delay in gonad development results from depletion of the salvage pathway product NAD+, whereas the uv1 cell necrosis and egg-laying defects result from accumulation of the substrate nicotinamide. Thus, regulation of both substrate and product level is key to the biological activity of PNC-1. We also find that diet probably affects the levels of these metabolites, as it affects phenotypes. Finally, we identified a secreted isoform of PNC-1 and confirmed its extracellular localization and functional activity in vivo. We demonstrate that nicotinamide phosphoribosyltransferase (Nampt), the equivalent enzyme in nicotinamide recycling to NAD+ in vertebrates,can functionally substitute for PNC-1. As Nampt is also secreted, we postulate an evolutionarily conserved extracellular role for NAD+biosynthetic enzymes during development and physiology.

Comparative Metabolomic Profiling Reveals That Dysregulated Glycolysis Stemming from Lack of Salvage NAD+ Biosynthesis Impairs Reproductive Development in Caenorhabditis elegans

“…We have revealed that the reproductive system as well as muscle development and function are particularly sensitive to loss of ability to synthesize NAD ϩ via a salvage pathway from nicotinamide and that these phenotypes are caused by the tissue-specific effects of both nicotinamide and nicotinic acid levels (12)(13)(14). In this study we demonstrate that salvage synthesis has a mild global negative effect on NAD ϩ levels but that mitochondrial function is preserved when salvage synthesis from nicotinamide (NAM) 2 is blocked.…”

“…Although NAMPT and nicotinamidase are distinct enzymes and co-exist only in select organisms (15), they have biologically comparable functions in consuming NAM and producing NAD ϩ . Human NAMPT can partially compensate for the loss of the C. elegans nicotinamidase pnc-1, demonstrating an equivalent biological role for the two enzymes (12). Finally NAD ϩ is produced from the essential amino acid tryptophan through the kynurenine pathway, which produces quinolinic acid that is converted to nicotinic acid mononucleotide via quinolinic acid phosphoribosyltransferase (21).…”

“…Finally NAD ϩ is produced from the essential amino acid tryptophan through the kynurenine pathway, which produces quinolinic acid that is converted to nicotinic acid mononucleotide via quinolinic acid phosphoribosyltransferase (21). The C. elegans genome does not encode an apparent homolog of quinolinic acid phosphoribosyltransferase (12,15). Thus, whether tryptophan can be used to synthesize NAD ϩ in C. elegans is unclear.…”

“…Mutation of the C. elegans pnc-1 nicotinamidase gene causes a variety of developmental and physiological defects (12,13,28). These phenotypes comprise three distinct classes: those that can be mimicked by supplementation of wild-type animals with the PNC-1 substrate NAM, those that are rescued by supplementation of mutants with the PNC-1 product NA, and those where both lack of NA production and accumulation of substrate make a contribution to the phenotypic outcome (12,13).…”

Non‐apoptotic cell death in Caenorhabditis elegans

“…However, a recent study revealed that the ku212 allele maps to the pnc-1 gene locus, which encodes for a nicotinamidase (van der Horst et al, 2007;Vrablik et al, 2009). Nicotinamidases are the first enzymes of the NAD þ salvage pathway in invertebrates, using nicotinamide (NAM) as a substrate (Magni et al, 1999).…”