Tissue nonspecific alkaline phosphatase improves bone quality but does not alleviate craniosynostosis in the FGFR2C342Y/+ mouse model of Crouzon syndrome
Craniosynostosis is the premature fusion of cranial bones. The goal of this study was to determine if delivery of recombinant tissue nonspecific alkaline phosphatase (TNAP) could prevent or diminish the severity of craniosynostosis in a C57BL/6 FGFR2C342Y/+ model of neonatal onset craniosynostosis or a BALB/c FGFR2C342Y/+ model of postnatal onset craniosynostosis. Mice were injected with a lentivirus encoding a mineral targeted form of TNAP immediately after birth. Cranial bone fusion as well as cranial bone volume, mineral content and density were assessed by micro computed tomography. Craniofacial shape was measured with calipers. Alkaline phosphatase, alanine amino transferase (ALT) and aspartate amino transferase (AST) activity levels were measured in serum. Neonatal delivery of TNAP diminished craniosynostosis severity from 94% suture obliteration in vehicle treated mice to 67% suture obliteration in treated mice, p<0.02) and the incidence of malocclusion from 82.4% to 34.7% (p<0.03), with no effect on cranial bone in C57BL/6 FGFR2C342Y/+ mice. In contrast, treatment with TNAP improved cranial bone volume (p< 0.01), density (p< 0.01) and mineral content (p< 0.01) but had no effect on craniosynostosis or malocclusion in BALB/c FGFR2C342Y/+ mice. These results indicate that perinatal recombinant TNAP enzyme therapy diminishes craniosynostosis severity in the C57BL/6 FGFR2C342Y/+ neonatal onset mouse model of Crouzon syndrome, and that effects of exogenous TNAP are genetic background dependent.