Neuronal injury leads to rapid, programmed disintegration of axons distal to the site of lesion. Much like other forms of axon degeneration (e.g. developmental pruning, toxic insult from neurodegenerative disorder), Wallerian degeneration associated with injury is preceded by spheroid formation along axons. The mechanisms by which injury leads to formation of spheroids and whether these spheroids have a functional role in degeneration remain elusive. Here, using neonatal mouse primary sympathetic neurons, we investigate the roles of players previously implicated in the progression of Wallerian degeneration in injury-induced spheroid formation. We find that intra-axonal calcium flux is accompanied by actin-Rho dependent growth of calcium rich axonal spheroids that eventually rupture, releasing material to the extracellular space prior to catastrophic axon degeneration. Importantly, after injury, Sarm1^−/− and DR6^−/−, but not Wld^s (excess NAD⁺) neurons, are capable of forming spheroids that eventually rupture, releasing their contents to the extracellular space to promote degeneration. Supplementation of exogenous NAD⁺ or expressing WLD^s suppresses Rho-dependent spheroid formation and degeneration in response to injury. Moreover, injured or trophically deprived Sarm1^−/− and DR6^−/−, but not Wld^s neurons, are resistant to degeneration induced by conditioned media collected from wild-type axons after spheroid rupture. Taken together, these findings place Rho-actin and NAD⁺ upstream of spheroid formation and may suggest that other mediators of degeneration, such as DR6 and SARM1, mediate post-spheroid rupture events that lead to catastrophic axon disassembly.

神经元损伤导致损伤部位远端轴突的快速、程序性崩解。与其他形式的轴突变性（例如发育性修剪、神经退行性疾病的毒性损伤）非常相似，与损伤相关的沃勒变性之前是沿轴突形成球状体。损伤导致球体形成的机制以及这些球体是否在退化中具有功能性作用仍然难以捉摸。在这里，我们使用新生小鼠原代交感神经元，研究先前在损伤诱导的球体形成中沃勒变性的进展中涉及的参与者的作用。我们发现轴突内钙通量伴随着最终破裂的富含钙的轴突球体的肌动蛋白-Rho 依赖性生长，在灾难性轴突退化之前将物质释放到细胞外空间。重要的是，受伤后，Sarm1 ^-/-和DR6 ^-/-，但不是Wld ^s（过量 NAD ⁺）神经元，能够形成最终破裂的球体，将其内容物释放到细胞外空间以促进退化。外源NAD的补充⁺或表达WLD^小号响应损伤的Rho禁止显示依赖球体形成和退化。此外，受伤或营养缺乏的 Sarm1 ^-/-和DR6 ^-/-，但不是Wld ^s神经元对从球体破裂后野生型轴突收集的条件培养基诱导的变性具有抵抗力。综上所述，这些发现将 Rho-actin 和 NAD ⁺置于球状体形成的上游，并且可能表明其他退化介质，如 DR6 和 SARM1，介导了导致灾难性轴突解体的球状体破裂后事件。