Exon skipping using phosphorodiamidate morpholino oligomers (PMOs) is a promising treatment strategy for Duchenne muscular dystrophy (DMD). The most significant limitation of these clinically used compounds is their lack of delivery systems that target muscles; thus, cell-penetrating peptides are being developed to enhance uptake into muscles. Recently, we reported that uptake of peptide-conjugated PMOs into myofibers was mediated by scavenger receptor class A (SR-A), which binds negatively charged ligands. However, the mechanism by which the naked PMOs are taken up into fibers is poorly understood. In this study, we found that PMO uptake and exon-skipping efficiency were promoted in dystrophin-deficient myotubes via endocytosis through a caveolin-dependent pathway. Interestingly, SR-A1 was upregulated and localized in juxtaposition with caveolin-3 in these myotubes and promoted PMO-induced exon skipping. SR-A1 was also upregulated in the skeletal muscle of mdx52 mice and mediated PMO uptake. In addition, PMOs with neutral backbones had negative zeta potentials owing to their nucleobase compositions and interacted with SR-A1. In conclusion, PMOs with negative zeta potential were taken up into dystrophin-deficient skeletal muscle by upregulated SR-A1. Therefore, the development of a drug delivery system targeting SR-A1 could lead to highly efficient exon-skipping therapies for DMD.

使用二氨基磷酸二氢吗啉代寡聚物（PMO）跳过外显子是一种针对杜兴氏肌营养不良症（DMD）的有前途的治疗策略。这些临床上使用的化合物最显着的局限性是它们缺乏靶向肌肉的递送系统。因此，正在开发穿透细胞的肽以增强对肌肉的摄取。最近，我们报道说，肽结合的PMO被肌纤维摄取是由清道夫受体A类（SR-A）介导的，它结合了带负电荷的配体。但是，对于将裸露的PMO吸收到纤维中的机理了解甚少。在这项研究中，我们发现肌营养不良蛋白缺陷型肌管中的PMO摄取和外显子跳跃效率通过小窝蛋白依赖性途径的内吞作用而被促进。有趣的是，SR-A1在这些肌管中被上调并与小窝蛋白3并列定位，并促进了PMO诱导的外显子跳跃。SR-A1在骨骼肌中也被上调mdx 52小鼠和介导的PMO摄取。此外，具有中性主链的PMO由于其核碱基组成而具有负Zeta电位，并且与SR-A1相互作用。总之，通过上调SR-A1将具有负Zeta电位的PMO吸收到肌营养不良蛋白缺陷的骨骼肌中。因此，针对SR-A1的药物输送系统的开发可能会导致DMD的高效外显子跳过疗法。