NAD to the rescue

NAD helps counteract energy leakage from severed axons, report Wang et al. on page 349.Recently, Araki et al. (Science. 305:1010–1013) showed that NAD protects axons from degeneration after injury, apparently by activating SIRT1, a nuclear deacetylase involved in aging. Now, Wang et al. show that NAD prevents degeneration independent of SIRT1 and works locally to protect membrane integrity.

Axons degenerate when they are cut from their cell body. However, neurons from mice are protected from degeneration when they overexpress either Nmnat1, which synthesizes NAD, or the Wld^s fusion protein that contains Nmnat1.

Wang et al. found that overexpression of Wld^s or Nmnat1 prevented a decrease of NAD, normally seen in axons after severing, and delayed degeneration. Moreover, addition of NAD to culture media delayed...