Forming a bridge made of functional axons to span the lesion is essential to reconstruct the motor circuitry following spinal cord injury (SCI). Dorsal root ganglion (DRG) axons are robust in axon growth and have been proved to facilitate the growth of cortical neurons in a process of axon-facilitated axon regeneration. However, whether DRG transplantation affects the axon outgrowth of spinal motor neurons (SMNs) that play crucial roles in motor circuitry remains unclear. We investigated the axonal growth patterns of co-cultured DRGs and SMN aggregates (SMNAs) taking advantage of a well-designed 3D-printed in vitro system. Chondroitin sulphate proteoglycans (CSPG) induced inhibitory matrix was introduced to imitate the inhibitory environment following SCI. Axonal lengths of DRG, SMNA or DRG & SMNA cultured on the permissive or CSPG induced inhibitory matrix were measured and compared. Our results indicated that under the guidance of full axonal connection generated from two opposing populations of DRGs, SMNA axons were growth-enhanced and elongated along the DRG axon bridge to distances that they could not otherwise reach. Quantitatively, the co-culture increased the SMNA axonal length by 32.1 %. Moreover, the CSPG matrix reduced the axonal length of DRGs and SMNAs by 46.2 % and 17.7 %, respectively. This inhibitory effect was antagonized by the co-culture of DRGs and SMNAs. Especially for SMNAs, they extended the axons across the CSPG-coating matrix, reached the lengths close to those of SMNAs cultured on the permissive matrix alone. This study deepens our understanding of axon-facilitated reconstruction of the motor circuitry. Moreover, the results support SCI treatment utilizing the enhanced outgrowth of axons to restore functional connectivity in SCI patients.

中文翻译：

---

与背根神经节共培养时脊髓运动神经元的轴突生长增强，拮抗生长抑制环境

形成由功能性轴突组成的桥来跨越病变对于脊髓损伤（SCI）后重建运动回路至关重要。背根神经节 (DRG) 轴突在轴突生长中具有强大的功能，并已被证明在轴突促进的轴突再生过程中促进皮质神经元的生长。然而，DRG 移植是否会影响在运动回路中发挥关键作用的脊髓运动神经元 (SMN) 的轴突生长仍不清楚。我们利用精心设计的 3D 打印体外系统研究了共培养的 DRG 和 SMN 聚集体 (SMNA) 的轴突生长模式。引入硫酸软骨素蛋白聚糖 (CSPG) 诱导的抑制基质来模拟 SCI 后的抑制环境。测量并比较在允许或 CSPG 诱导的抑制基质上培养的 DRG、SMNA 或 DRG & SMNA 的轴突长度。我们的结果表明，在两个相反的 DRG 群体产生的完整轴突连接的指导下，SMNA 轴突生长增强，并沿着 DRG 轴突桥延伸到它们无法达到的距离。从数量上看，共培养使 SMNA 轴突长度增加了 32.1%。此外，CSPG 矩阵使 DRG 和 SMNA 的轴突长度分别减少了 46.2% 和 17.7%。这种抑制作用被 DRG 和 SMNA 的共培养所拮抗。特别是对于 SMNA，他们将轴突延伸到 CSPG 涂层基质上，达到了接近仅在许可基质上培养的 SMNA 的长度。这项研究加深了我们对轴突促进运动电路重建的理解。此外，这些结果支持利用轴突生长的增强来恢复 SCI 患者的功能连接的 SCI 治疗。