FLNB and TTC26 target ciliary hedgehog signaling to mediate extracellular matrix homeostasis of intervertebral disc in adolescent idiopathic scoliosis Running Title：FLNB and TTC26 regulate ntervertebral disc degeneration

Variable recurrence risk and curve manifestations in adolescent idiopathic scoliosis (AIS) has been ascribed to the oligogenic effect of multiple genes. However, evidence to support this hypothesis is currently lacking. In this study, we generated mice carrying double heterozygous mutations by injecting mouse androgenic haploid embryonic stem cells with mutant Flnb and Ttc26 into oocytes. The double heterozygous mutant mice exhibited IS-like phenotypes. Combined knockdown of FLNB and TTC26 resulted in dysregulated extracellular matrix (ECM) homeostasis of intervertebral disc (IVD) consistent with the analysis of the nucleus pulposus (NP) tissues from AIS patients. In vitro evidence indicated that FLNB and TTC26 co-regulated nucleus pulposus cells ECM metabolism via the hedgehog pathway (Hh). Mechanically, TTC26 transported the protein arginine methyltransferases 7 (PRMT7) into primary cilia where PRMT7 methylates GLI family zinc finger 2 (GLI2), and FLNB imported methylated GLI2 into nucleus through direct interaction. Furthermore, deletion of Ptch1 or Sufu stimulated the Hh signaling to rescue the metabolic disorder in Flnb ^−/+ ; Ttc26 ^−/+ discs. Overall, these results indicate that FLNB and TTC26 maintain IVD ECM hemostasis via Hh-GLI2 axis, and demonstrate that IVD may be involved the etiology of AIS.