Neuromuscular electrical stimulation (NMES) is a well-established therapeutic approach for chronic wounds. Conventionally, NMES involves direct electrode contact with wounds or adjacent healthy skin; however, it is limited by the need for wound exposure and increased pain. Our preliminary study demonstrated the innovative application of remote NMES (rNMES) to the skeletal muscle of the distal calf, demonstrating the potential to accelerate wound healing in remote areas. rNMES is effective in human clinical trials in our previous work, although the underlying mechanisms remain unclear. As rNMES is often used to stimulate muscle contraction in long-term bedridden patients, we analyzed GEO database data and found that exercise promotes midkine (MDK) expression in muscle, a small secreted heparin-binding protein that interacts with multiple cell surface receptors to promote growth. MDK significantly enhanced macrophage efferocytosis in a low-density lipoprotein receptor-related protein 1 (LRP1)-dependent manner. Our findings demonstrate that rNMES upregulates MDK expression in skeletal muscles through the AMPK-ERK axis, facilitating its delivery to wounds through the circulatory system and promoting LRP1-mediated efferocytosis of apoptotic cells, thereby expediting wound healing.

Keywords: LRP1; MDK; efferocytosis; rNMES; wound healing.

神经肌肉电刺激（NMES）是治疗慢性伤口的一种成熟疗法。传统上，NMES需要直接将电极与伤口或邻近的健康皮肤接触；然而，这种方法受限于必须暴露伤口并且可能会增加疼痛感。我们的初步研究展示了一种创新的应用方法：远程NMES（rNMES），通过刺激小腿远端骨骼肌来促进远处伤口的愈合。在我们之前的工作中发现，rNMES对人体临床试验有效，尽管其背后的机制尚不清楚。由于rNMES常被用于长期卧床患者的肌肉收缩刺激，我们分析了GEO数据库的数据，并发现运动可以增加肌肉中的中期蛋白（MDK）表达，这是一种与多种细胞表面受体相互作用以促进生长的小型分泌性肝素结合蛋白。MDK显著增强了低密度脂蛋白受体相关蛋白1 (LRP1)依赖性的巨噬细胞摄取凋亡细胞的能力。我们的研究结果表明，rNMES通过AMPK-ERK轴上调骨骼肌中的MDK表达，从而将其传递到伤口部位并通过血液循环促进LRP1介导的凋亡细胞清除作用，进而加速了伤口愈合。

关键词：LRP1；MDK；efferocytosis；rNMES；伤口愈合。