Nicotinamide phosphoribosyltransferase regulates cell survival through NAD+ synthesis in cardiac myocytes.
BACKGROUND
NAD+ acts not only as a cofactor for cellular respiration but also as a substrate for NAD(+)-dependent enzymes, such as Sirt1. The cellular NAD+ synthesis is regulated by both the de novo and the salvage pathways. Nicotinamide phosphoribosyltransferase (Nampt) is a rate-limiting enzyme in the salvage pathway.


OBJECTIVE
Here we investigated the role of Nampt in mediating NAD+ synthesis in cardiac myocytes and the function of Nampt in the heart in vivo.


RESULTS
Expression of Nampt in the heart was significantly decreased by ischemia, ischemia/reperfusion and pressure overload. Upregulation of Nampt significantly increased NAD+ and ATP concentrations, whereas downregulation of Nampt significantly decreased them. Downregulation of Nampt increased caspase 3 cleavage, cytochrome c release, and TUNEL-positive cells, which were inhibited in the presence of Bcl-xL, but did not increase hairpin 2-positive cells, suggesting that endogenous Nampt negatively regulates apoptosis but not necrosis. Downregulation of Nampt also impaired autophagic flux, suggesting that endogenous Nampt positively regulates autophagy. Cardiac-specific overexpression of Nampt in transgenic mice increased NAD+ content in the heart, prevented downregulation of Nampt, and reduced the size of myocardial infarction and apoptosis in response to prolonged ischemia and ischemia/reperfusion.


CONCLUSIONS
Nampt critically regulates NAD+ and ATP contents, thereby playing an essential role in mediating cell survival by inhibiting apoptosis and stimulating autophagic flux in cardiac myocytes. Preventing downregulation of Nampt inhibits myocardial injury in response to myocardial ischemia and reperfusion. These results suggest that Nampt is an essential gatekeeper of energy status and survival in cardiac myocytes.
Hsu
Chiao-Po
CP
Cardiovascular Research Institute, UMDNJ-Newark, 185 S Orange Ave, MSB G609, Newark, NJ 07103, USA.
Oka
Shinichi
S
Shao
Dan
D
Hariharan
Nirmala
N
Sadoshima
Junichi
J
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D001343:Autophagy; D053148:Caspase 3 / Q000378:metabolism; D002478:Cells, Cultured; D045304:Cytochromes c; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D004195:Disease Models, Animal; D004734:Energy Metabolism; D051379:Mice; D008822:Mice, Transgenic; D017202:Myocardial Ischemia / Q000201:enzymology / Q000473:pathology; D032383:Myocytes, Cardiac / Q000201:enzymology* / Q000473:pathology; D009243:NAD / Q000378:metabolism*; D054409:Nicotinamide Phosphoribosyltransferase / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015427:Reperfusion Injury / Q000201:enzymology / Q000473:pathology; D051020:bcl-X Protein / Q000378:metabolism
D016207:Cytokines; D012333:RNA, Messenger; D051020:bcl-X Protein; D009243:NAD; D000255:Adenosine Triphosphate; D045304:Cytochromes c; D054409:Nicotinamide Phosphoribosyltransferase; C495867:nicotinamide phosphoribosyltransferase, mouse; C504970:nicotinamide phosphoribosyltransferase, rat; C505410:Casp3 protein, rat; D053148:Caspase 3