The morphological discrepancy of neuromuscular junctions between bilateral paraspinal muscles in patients with adolescent idiopathic scoliosis: A quantitative immunofluorescence assay

Introduction

Prior studies suggested that neuromuscular factors might be involved in the pathogenesis of adolescent idiopathic scoliosis (AIS). The neuromuscular junction (NMJ) is the important pivot where the nervous system interacts with muscle fibers, but it has not been well characterized in the paraspinal muscles of AIS. This study aims to perform the quantitative morphological analysis of NMJs from paraspinal muscles of AIS.

Methods

AIS patients who received surgery in our center were prospectively enrolled. Meanwhile, age-matched congenital scoliosis (CS) and non-scoliosis patients were also included as controls. Fresh samples of paraspinal muscles were harvested intraoperatively. NMJs were immunolabeled using different antibodies to reveal pre-synaptic neuronal architecture and post-synaptic motor endplates. A confocal microscope was used to acquire z-stack projections of NMJs images. Then, NMJs images were analyzed on maximum intensity projections using ImageJ software. The morphology of NMJs was quantitatively measured by a standardized ‘NMJ-morph’ workflow. A total of 21 variables were measured and compared between different groups.

Results

A total of 15 AIS patients, 10 CS patients and 5 normal controls were enrolled initially. For AIS group, NMJs in the convex side of paraspinal muscles demonstrated obviously decreased overlap when compared with the concave side (34.27% ± 8.09% vs. 48.11% ± 10.31%, p = 0.0036). However, no variables showed statistical difference between both sides of paraspinal muscles in CS patients. In contrast with non-scoliosis controls, both sides of paraspinal muscles in AIS patients demonstrated significantly smaller muscle bundle diameters.

Conclusions

This study first elucidated the morphological features of NMJs from paraspinal muscles of AIS patients. The NMJs in the convex side showed smaller overlap for AIS patients, but no difference was found in CS. This proved further evidence that neuromuscular factors might contribute to the mechanisms of AIS and could be considered as a novel potential therapeutic target for the treatment of progressive AIS.