The new insight into extracellular NAD+ degradation-the contribution of CD38 and CD73 in calcific aortic valve disease

Nicotinamide adenine dinucleotide (NAD(+)) is crucial for cell energy metabolism and many signalling processes. Recently, we proved the role of ecto-enzymes in controlling adenine nucleotide-dependent pathways during calcific aortic valve disease (CAVD). This study aimed to investigate extracellular hydrolysis of NAD(+) and mononucleotide nicotinamide (NMN) in aortic valves and aorta fragments of CAVD patients and on the inner aortic surface of ecto-5 '-nucleotidase knockout mice (CD73-/-). Human non-stenotic valves (n = 10) actively converted NAD(+) and NMN via both CD73 and NAD(+)-glycohydrolase (CD38) according to our analysis with RP-HPLC and immunofluorescence. In stenotic valves (n = 50), due to reduced CD73 activity, NAD(+) was degraded predominantly by CD38 and additionally by ALP and eNPP1. CAVD patients had significantly higher hydrolytic rates of NAD(+) (0.81 +/- 0.07 vs 0.56 +/- 0.10) and NMN (1.12 +/- 0.10 vs 0.71 +/- 0.08 nmol/min/cm(2)) compared with controls. CD38 was also primarily engaged in human vascular NAD(+) metabolism. Studies using specific ecto-enzyme inhibitors and CD73-/- mice confirmed that CD73 is not the only enzyme involved in NAD(+) and NMN hydrolysis and that CD38 had a significant contribution to these pathways. Modifications of extracellular NAD(+) and NMN metabolism in aortic valve cells may be particularly important in valve pathology and could be a potential therapeutic target.