Deletion of a Pax1 sex-associated genomic region associated with adolescent idiopathic scoliosis leads to disc degeneration, instability, and vertebral rotation in mice

Background Adolescent idiopathic scoliosis (AIS) is a complex spinal deformity characterized by three-dimensional curvature of the spine with an unknown etiology. Previous genome-wide association studies have identified a single-nucleotide polymorphism (rs6137473) located downstream of PAX1, which is significantly associated with female AIS risk. Methods To investigate the role of this region in spinal development and AIS pathogenesis, we generated a mouse model with deletion of a nearby conserved sex-associated region (Pax1-SARΔ). Spines were examined by both micro-CT and histology. Gene expression analysis (by RNA-sequencing and quantitative PCR) was carried out on E12.5 and E18.5 developing spines. Glycosaminoglycan (GAG) content was also measured by high-performance liquid chromatography. Results Micro-CT analysis revealed increased vertebral rotation at T4 in female Pax1-SARΔ mice at 4 months and at T9 in male Pax1-SARΔ mice at 6 months, along with kyphotic and lordotic sagittal curvatures. Histological examination revealed significant intervertebral disc degeneration, with the most severe changes observed in the female Pax1-SARΔ mice. GAG analysis found decreased chondroitin sulfate and dermatan sulfate content in male and female Pax1-SARΔ mice. Gene expression analysis at E12.5 showed upregulation of Pax1, Stat3, Ar, Foxa2, and Nkx2.2, while RNA-sequencing at E18.5 revealed sex-dependent changes in gene expression related to extracellular matrix components, immune and inflammatory responses, and scoliosis. Conclusion: These findings highlight the pivotal role of the Pax1 sex-associated genomic region in the development and maintenance of functional cartilage, extracellular matrix integrity, and intervertebral disc health, offering insights into the mechanisms underlying spinal degeneration and instability in AIS.