A New Wnt1 Mutant Rat Model of Osteogenesis Imperfecta and Its Application in AAV9-Mediated Gene Therapy

Osteogenesis imperfecta (OI) is a genetically and clinically heterogeneous bone disorder, with more than 20 genes contributing to OI development. Previously, we identified WNT1 c.620G > A (p.Arg207His) mutation among Chinese patients with autosomal recessive OI (AR-OI). This study aims at investigating the causative role of WNT1 deficiency in OI and evaluate whether AAV-based gene therapy could ameliorate bone abnormalities. We generated and analyzed the Wnt1^R207H/R207H rat model. The AAV9-Wnt1 virus was delivered via direct intraosseous injection into the femoral marrow cavity of the OI rats to evaluate its therapeutic potential. The homozygous Wnt1^R207H/R207H rat recapitulated key features of AR-OI, including fractures, reduced bone mass, growth retardation, decreased survival rate, increased osteoclast numbers, diminished osteoblast function and mineralization capacity, compared with heterozygous and wild-type littermates. In vitro, Wnt1 overexpression in osteoblasts promoted osteoblast activity and bone mineralization. Furthermore, AAV9-Wnt1 treatment in OI rats resulted in significant recovery of bone density and mechanical strength, stimulation of osteoblast activity, suppression of osteoclast activity, and upregulation of Type I collagen expression. Our study demonstrates that WNT1 c.620G > A (p.Arg207His) is pathogenic, and confirms that AAV-mediated Wnt1 gene therapy represents a promising strategy for treating OI caused by WNT1 mutations.