Depletion of the central metabolite NAD leads to oncosis mediated cell death [Metabolism]

October 29th, 2014 by Del Nagro, C., Xiao, Y., Rangell, L., Reichelt, M., O'Brien, T.

Depletion of the central metabolite NAD in cells results in broad metabolic defects leading to cell death and is a proposed novel therapeutic strategy in oncology. There is however a limited understanding of the underlying mechanisms that connect disruption of this central metabolite with cell death. Here we utilize GNE-617, a small molecule inhibitor of NAMPT, a rate-limiting enzyme required for NAD generation, to probe the pathways leading to cell death following NAD depletion. In all cell lines examined NAD was rapidly depleted (average t1/2 of 8.1hr) following NAMPT inhibition. Concurrent with NAD depletion, there was a decrease in both cell proliferation and motility, which we attribute to reduced activity of NAD-dependent deacetylases as cells fail to deacetylate α-tubulin-K40 and histone H3-K9. Following depletion of NAD by >95%, cells lose the ability to regenerate ATP. Cell lines with a slower rate of ATP depletion (average t1/2 of 45hr) activate caspase-3 and show evidence of apoptosis and autophagy whereas cell lines with rapid depletion ATP (average t1/2 of 32 hr) do not activate caspase-3 or show signs of apoptosis or autophagy. However, the predominant form of cell death in all lines is oncosis, which is driven by the loss of plasma membrane homeostasis once ATP levels are depleted by >20-fold. Thus, our work illustrates the sequence of events that occurs in cells following depletion of a key metabolite, and reveals that cell death due to loss of NAD is primarily driven by the inability of cells to regenerate ATP.