Abstract
Prior studies showed that polyglutamine-expanded androgen receptor (AR) is aberrantly acetylated and that deacetylation of the mutant AR by overexpression of nicotinamide adenine dinucleotide–dependent (NAD+-dependent) sirtuin 1 is protective in cell models of spinal and bulbar muscular atrophy (SBMA). Based on these observations and reduced NAD+ in muscles of SBMA mouse models, we tested the therapeutic potential of NAD+ restoration in vivo by treating postsymptomatic transgenic SBMA mice with the NAD+ precursor nicotinamide riboside (NR). NR supplementation failed to alter disease progression and had no effect on increasing NAD+ or ATP content in muscle, despite producing a modest increase of NAD+ in the spinal cords of SBMA mice. Metabolomic and proteomic profiles of SBMA quadriceps muscles indicated alterations in several important energy-related pathways that use NAD+, in addition to the NAD+ salvage pathway, which is critical for NAD+ regeneration for use in cellular energy production. We also observed decreased mRNA levels of nicotinamide riboside kinase 2 (Nmrk2), which encodes a key kinase responsible for NR phosphorylation, allowing its use by the NAD+ salvage pathway. Together, these data suggest a model in which NAD+ levels are significantly decreased in muscles of an SBMA mouse model and intransigent to NR supplementation because of decreased levels of Nmrk2.
Authors
Danielle DeBartolo, Frederick J. Arnold, Yuhong Liu, Elana Molotsky, Hsin-Yao Tang, Diane E. Merry
Figure 3
NAD+ and ATP levels are substantially reduced in the muscle but not in the spinal cord of SBMA mice.
