Project Summary
Paternal age is positively correlated with reduced sperm chromatin quality and higher numbers of DNA
strand breaks which can negatively affect pregnancy outcome and child development. There is a normal
aging-related decline of NAD levels in humans that may provide a plausible explanation for reduced sperm
quality in aging men, but this hypothesis has been difficult to test due to the absence of suitable laboratory
animal models. To address this important problem, we developed a transgenic mouse with inducible
overexpression of the enzyme hACMSD, which leads to an acquired dependency of the animals on dietary
intake of vitamin B3 (niacin) for their NAD synthesis (ANDY mouse, Cell Reports, 2018), similar to humans.
Dietary niacin restriction of ANDY mice leads to adjustably reduced NAD levels, reminiscent of niacin
deficiency possible in humans. Our preliminary data show indeed that suboptimal NAD levels in ANDY mice
resulted in elevated numbers of DNA strand breaks and poor chromatin maturation in sperm, which were
reversible by oral niacin supplementation, indicating that niacin may be a micronutrient of previously
unrecognized importance for male reproduction. The main objective of this project is to test the overarching
hypothesis, that low metabolic NAD+ levels lead to reduced chromatin quality and DNA integrity in sperm,
using the ANDY mouse model. To this end, we propose to 1) measure the extent to which reduced
glutathione (GSH) levels resulting from low NADPH stores in niacin-deficient ANDY spermatids cause
elevated oxidative stress. Characterization of open DNA ends in sperm and spermatids using a sequencing
approach will determine the contribution of oxidative DNA damage to sperm; 2) determine the impact of
niacin deficiency on the activity of NAD-dependent enzymes involved in sperm chromatin development,
such as ADP-ribose transferases and sirtuins, and how that results in poor chromatin quality that makes
sperm vulnerable to exogenous DNA damage. We will also evaluate reversibility of NAD deficiency by
nutritional niacin supplementation to increase testicular NAD and NADP levels and to correct poor sperm
quality in ANDY mice. Furthermore, funding of this project would enhance the infrastructure at Utah State
University needed to provide undergraduate students, including from underrepresented minorities, with
biochemical and biomedical research opportunities. These will enable students, including underrepresented
minority and beginning students, to experience a wide range of modern research techniques and to acquire
skills of critical thinking, data evaluation and science presentation, which is a training they would otherwise
not have access to.