The Neurogenic Abnormities of Paraspinal Muscles Lead to Asymmetry of Fibre Types in Adolescent Idiopathic Scoliosis

The aetiology of adolescent idiopathic scoliosis (AIS) is not clear, and may involve disorders in multiple systems. This study aims to perform the morphological and molecular analysis of neuromuscular junctions (NMJs) and explore the asymmetry of paraspinal muscles in AIS. We collected paraspinal muscles from AIS patients during surgery and also enrolled congenital scoliosis (CS) and non-scoliosis patients as controls. We performed immunofluorescence staining of NMJs for morphological analysis. Then, we extracted NMJs regions for further validation at the molecular level. We also explored the neurogenic abnormalities in the convex side and compared the asymmetry of paraspinal muscles. Morphological analysis of NMJs showed that the nerve terminal-related variables in the convex side were significantly decreased. The expression of denervation markers was increased in the synapse-rich regions. The expression of denervation markers in the convex paraspinal muscles was also significantly increased. Compared with CS and non-scoliosis patients, paraspinal muscles of AIS exhibited the transformation of fibre types, characterised by an increase in the proportion of type I fibres in the convex side. The phenomenon of fibre-type grouping was also noted, confirming the presence of neurogenic abnormalities. This study first investigated the morphological and molecular disorders of NMJs in the paraspinal muscles from AIS patients. We found that the neurogenic abnormalities existed in the convex side of the paraspinal muscle, which could lead to the conversion and grouping of fibre types. This resulted in an imbalance of bilateral paraspinal muscles and might be a potential driver of scoliosis.