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SARM1 activation triggers axon degeneration locally via NAD+ destruction

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Science  24 Apr 2015:
Vol. 348, Issue 6233, pp. 453-457
DOI: 10.1126/science.1258366

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SARM1-driven axon degeneration

Axons, the long protrusions of nerve cells, are programmed to self-destruct under certain conditions that occur during development, stress, or disease states. Gerdts et al. outline a biochemical mechanism that controls such axon degeneration. The authors designed versions of SARM1 (sterile alpha and TIR motif—constraining 1) that could be activated or inhibited in cells. Their experiments showed that the activation of SARM1 was necessary and sufficient to cause axon destruction in cultured mouse neurons. SARM1-mediated destruction was associated with depletion of the metabolic cofactor NAD+ from cells.

Science, this issue p. 453

Abstract

Axon degeneration is an intrinsic self-destruction program that underlies axon loss during injury and disease. Sterile alpha and TIR motif–containing 1 (SARM1) protein is an essential mediator of axon degeneration. We report that SARM1 initiates a local destruction program involving rapid breakdown of nicotinamide adenine dinucleotide (NAD+) after injury. We used an engineered protease-sensitized SARM1 to demonstrate that SARM1 activity is required after axon injury to induce axon degeneration. Dimerization of the Toll–interleukin receptor (TIR) domain of SARM1 alone was sufficient to induce locally mediated axon degeneration. Formation of the SARM1 TIR dimer triggered rapid breakdown of NAD+, whereas SARM1-induced axon destruction could be counteracted by increased NAD+ synthesis. SARM1-induced depletion of NAD+ may explain the potent axon protection in Wallerian degeneration slow (Wlds) mutant mice.

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