Fig. 4.

Effects of NAD+ breakdown on axon degeneration. A) Diagram of NAD+ manipulation using Tnkp dimerization. NAD+ loss induced by FkbpF36V-Tnkp dimerization is blocked by Tankyrase inhibitor XAV939 or NR and is exacerbated by FK866. B) Axon degeneration in response to NAD+ depletion by dimerized Tnkp and FK866 after 24 hours (bar d) and inhibition by Tankyrase inhibitor XAV939 (100 nM; bar e). Representative α-Tubulin-stained axons corresponding to bars b and d are shown; scale bar = 50 micrometers. C) Effect of NAD+ depletion by dimerized Tnkp + FK866 on axon degeneration in Sarm1−/− uninjured axons (bar b) or isolated (cut) Sarm1−/− axons (bar d). D) Effect of sTIR dimerization on endogenous (dotted lines) and exogenously introduced (solid lines) NAD+ or NaAD (control) in HTir cells. NaAD is undetectable in non-electroporated cells. E) Conversion of ¹⁴C-NAD+ in HTir cells to Nam 15 minutes after SARM1 TIR dimerization. NAD+ and Nam from cell extracts and extracellular media were resolved by thin layer chromatography. F) Top: effect of the PARP inhibitor olaparib (100 nM) on NAD+ loss induced by 1 mM H₂O₂ (10 min) or sTIR dimerization (10 min). Bottom: PAR formation after H₂O₂ treatment or sTIR dimerization in HTir cells expressing PARG shRNA and inhibition by olaparib. Error bars = SEM; * p < 0.01; one way ANOVA with Tukey’s post-hoc test.