Effects of different frequency electroacupuncture on mitochondrial function and oxidative stress injury in quadriceps femoris muscle of rabbits with anterior cruciate ligament injury

Abstract

BACKGROUND: Oxidative stress is one of the potential factors contributing to muscle atrophy following anterior cruciate ligament injury. Alleviating skeletal muscle fatigue facilitates proprioceptive recovery, thereby accelerating rehabilitation after anterior cruciate ligament injury. Improving mitochondrial function helps mitigate skeletal muscle fatigue-related damage. OBJECTIVE: To verify that electroacupuncture at different frequencies alleviates skeletal muscle oxidative stress damage and improves mitochondrial function in rabbits, thereby reducing skeletal muscle fatigue, restoring proprioceptive function, and accelerating rehabilitation following anterior cruciate ligament injury. METHODS: Twenty-four healthy New Zealand rabbits were randomly divided into blank group, model group, low-frequency electroacupuncture group, and high-frequency electroacupuncture group, with 6 rabbits in each group. The model group, low-frequency electroacupuncture group, and high-frequency electroacupuncture group were used to construct a knee anterior cruciate ligament injury model. In the low-frequency and high-frequency electroacupuncture groups, electroacupuncture was applied to the acupoints Xuehai and Liangqiu on the affected knee joint 7 days after modeling. The blank and model groups were only grasped and fixed without electroacupuncture intervention, once daily for 21 consecutive days. After intervention, ELISA was used to detect the levels of superoxide dismutase, succinate dehydrogenase, and malondialdehyde in the quadriceps femoris; western blot was used to detect the protein expression levels of silent information regulator 2-related enzyme 1, peroxisome proliferator-activated receptor gamma coactivator 1 alpha, and mitochondrial transcription factor A in skeletal muscle tissue, as well as the mRNA expression of silent information regulator 2-related enzyme 1, peroxisome proliferator-activated receptor gamma coactivator 1 alpha, nuclear respiratory factor 1, and mitochondrial transcription factor A. RESULTS AND CONCLUSION: After anterior cruciate ligament injury, the level of superoxide dismutase in the quadriceps femoris of rabbits increased, the level of succinate dehydrogenase decreased, and the concentration of malondialdehyde increased; the protein expressions of silent information regulator 2-related enzyme 1, peroxisome proliferator-activated receptor gamma coactivator 1 alpha, and mitochondrial transcription factor A decreased; the mRNA expressions of silent information regulator 2-related enzyme 1, peroxisome proliferator-activated receptor gamma coactivator 1 alpha, nuclear respiratory factor 1, and mitochondrial transcription factor A were significantly downregulated. After electroacupuncture intervention, the concentration of malondialdehyde in the affected quadriceps femoris decreased, the activities of superoxide dismutase and succinate dehydrogenase increased, and the protein expressions of silent information regulator 2-related enzyme 1, peroxisome proliferator-activated receptor gamma coactivator 1 alpha, and mitochondrial transcription factor A increased; the mRNA expressions of mitochondrial biogenesis-related genes such as silent information regulator 2-related enzyme 1, peroxisome proliferator-activated receptor gamma coactivator 1 alpha, nuclear respiratory factor 1, and mitochondrial transcription factor A increased, and the low-frequency electroacupuncture group was superior to the high-frequency electroacupuncture group. These results indicate that electroacupuncture can reduce oxidative stress damage in skeletal muscle after anterior cruciate ligament injury by increasing the contents of superoxide dismutase and succinate dehydrogenase and decreasing the content of malondialdehyde; and improve mitochondrial function by regulating the expression of proteins related to the silent information regulator 2-related enzyme 1/peroxisome proliferator-activated receptor gamma coactivator 1 alpha signaling pathway and mitochondrial biogenesis-related genes, thereby accelerating rehabilitation after anterior cruciate ligament injury.

1. Introduction

The anterior cruciate ligament originates from the anterior medial aspect of the tibial intercondylar eminence, attaches to the anterior horn of the lateral meniscus, and runs obliquely posteriorly and superiorly laterally, with fibers fanning out to attach to the medial aspect of the lateral femoral condyle [1]. It primarily controls anterior and rotational stability of the knee joint [2], resisting anterior translation of the tibia relative to the femur, and works with the posterior cruciate ligament to balance anteroposterior tension and stabilize the knee. Sports injuries account for 70% of anterior cruciate ligament injuries, mainly caused by knee valgus, external rotation, and hyperextension [3]. Anterior cruciate ligament injuries often combine with medial collateral ligament and meniscus injuries, leading to mechanical imbalance of the knee joint and destruction of proprioceptors, resulting in decreased proprioception in both knees [4], further affecting knee stability and greatly reducing patients' motor function and quality of life [5-8]. Anterior cruciate ligament reconstruction is the preferred clinical option to restore knee stability; however, postoperative proprioceptor reduction affects position sense and motor signal transmission, leading to knee instability, slow reaction, and decreased dynamic balance, and postoperative mechanoreceptor damage inhibits quadriceps activation [9]. Therefore, proprioceptive recovery is key to functional rehabilitation after anterior cruciate ligament reconstruction [10].

Skeletal muscle is the core of human movement, and its functional state is directly related to athletic performance. Good neuromuscular function is the basic guarantee for maintaining dynamic joint stability and reducing sports injuries during exercise [11]. Researchers have induced knee extension fatigue using isokinetic strength testing systems [12]; when the maximum knee extension torque drops to 30%, the knee flexion angle during landing significantly decreases, and at smaller knee flexion angles, larger extension torque relatively increases the tension on the anterior cruciate ligament, increasing the risk of rupture [13].