NAD ⁺ repletion improves muscle function in muscular dystrophy and counters global PARylation

Abstract

Neuromuscular diseases are often caused by inherited mutations that lead to progressive skeletal muscle weakness and degeneration. In diverse populations of normal healthy mice, we observed correlations between the abundance of mRNA transcripts related to mitochondrial biogenesis, the dystrophin-sarcoglycan complex, and nicotinamide adenine dinucleotide (NAD+) synthesis, consistent with a potential role for the essential cofactor NAD+ in protecting muscle from metabolic and structural degeneration. Furthermore, the skeletal muscle transcriptomes of patients with Duchene’s muscular dystrophy (DMD) and other muscle diseases were enriched for various poly[adenosine 5’-diphosphate (ADP)–ribose] polymerases (PARPs) and for nicotinamide N-methyltransferase (NNMT), enzymes that are major consumers of NAD+ and are involved in pleiotropic events, including inflammation. In the mdx mouse model of DMD, we observed significant reductions in muscle NAD+ levels, concurrent increases in PARP activity, and reduced expression of nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme for NAD+ biosynthesis. Replenishing NAD+ stores with dietary nicotinamide riboside supplementation improved muscle function and heart pathology in mdx and mdx/Utr−/− mice and reversed pathology in Caenorhabditis elegans models of DMD. The effects of NAD+ repletion in mdx mice relied on the improvement in mitochondrial function and structural protein expression (α-dystrobrevin and δ-sarcoglycan) and on the reductions in general poly(ADP)-ribosylation, inflammation, and fibrosis. In combination, these studies suggest that the replenishment of NAD+ may benefit patients with muscular dystrophies or other neuromuscular degenerative conditions characterized by the PARP/NNMT gene expression signatures.

Therapeutic Potential of NAD-Boosting Molecules: The In Vivo Evidence

“…NR also increases the number and quality of muscle stem cells (MuSC) and enhances muscle regeneration in old mice, in part, by improving mitochondrial function and preventing MuSC senescence (Zhang et al, 2016). In the context of muscular dystrophy models, NR improves mobility in dystrophic C. elegans mutants (Ryu et al, 2016), NAD + supplementation of zebrafish reduces the percentage of detached muscle fibers and increases mobility (Goody et al, 2012), and in the MDX mouse, NR improves mitochondrial function, recovery from muscle injury, and running capacity (Ryu et al, 2016). …”

Redox Control of Skeletal Muscle Regeneration

“…Moreover, MuSCs exhibit an increased ability to differentiate in vitro and to express the differentiation markers myogenin and myosin heavy chain, indicative of their good regenerative potential (298). Finally, mdx mice supplemented for 10 weeks with nicotinamide riboside exhibit an increased number of MuSCs while muscle regeneration is improved, indicating that nicotinamide riboside also prevents MuSC senescence in muscular dystrophy (287,361), as it does in aging muscle (see Section X-B-2: In aging) (Fig. 14).…”

“…Inversely, after an acute injury, inducing a compartment-specific increase of the NAD + /NADH ratio (using LbNOX water-forming NOX from Lactobacillus brevis) allowed to decipher the NAD + /NADH ratio-driven signaling and to improve proliferative and metabolic defects in mitochondrial-deficient cells (323). Several studies recently confirmed that the redox couple NAD + /NADH is a privileged target to improve cell and tissue homeostasis, including in aged and diseased skeletal muscle (see Section X.B) (110,287,361).…”

The role of caloric load and mitochondrial homeostasis in the regulation of the NLRP3 inflammasome

“…Interestingly, other groups have found a similar inhibitory effect of NAD + repletion by NR supplementation on hepatosteatosis, hepatic inflammation and NLRP3 inflammasome activation in mice [76, 116, 117]. Whether NR could function to suppress the NLRP3 inflammasome has the potential to be explored as a therapeutic agent, given its myriad of other beneficial effects in vivo [118–121]. Accordingly, NAD + repletion by other compounds such as nicotinamide mononucleotide (NMN) similarly ameliorated age-associated adipose tissue inflammation [122], HFD-induced liver inflammation [37] and fructose-rich diet-induced pancreatic islet β cell IL-1β secretion and dysfunction in mice [123].…”

“…Accordingly, NAD + repletion by other compounds such as nicotinamide mononucleotide (NMN) similarly ameliorated age-associated adipose tissue inflammation [122], HFD-induced liver inflammation [37] and fructose-rich diet-induced pancreatic islet β cell IL-1β secretion and dysfunction in mice [123]. These effects of NR and NMN appear to be largely mediated by SIRT1 and/ or SIRT3 [117, 121, 124]. Not surprisingly, resveratrol, the polyphenol present in the skin of grapes, another sirtuin activator, also inhibits NLRP3 inflammasome activation in mice by preserving mitochondrial function, and protects against hepatosteatosis, renal inflammation and LPS-induced lung injury [125–127].…”