TNAP and PHOSPHO1 Function Synergistically to Afford Critical Control Over the Mineralization of the Postnatal Murine...

Biomineralization is essential for skeletal integrity, yet the synergistic roles of tissue non-specific alkaline phosphatase (TNAP) and PHOSPHO1 in postnatal bone remain unclear. We generated a novel murine model with Prx1-driven deletion of Alpl (Alpl^Prx1/Prx1) on a global Phospho1^-/- background, circumventing the perinatal lethality associated with dual global deletion and premature death of Alpl global knockouts. Multi-modal spatial phenotyping of the limbs revealed that mice lacking both TNAP and PHOSPHO1 exhibit distinct mineralization defects and altered anatomical structures at postnatal day 1 (PN1) and 3-weeks of age. Although viable, these mice did not thrive due to reduced size; thus further investigations were conducted on mice with heterozygous deletion of TNAP (Alpl^wt/Prx1;Phospho1^-/-). Although smaller than wild-types at PN1 and 3 weeks old, these mice preserved gross limb structure and the single, functioning Alpl allele rescued biomineralization loss following dual phosphatase deletion. In 6-week animals, compromised epiphyses and metaphyses were only observed in Alpl^Prx1/Prx1 animals. Conversely, diaphyseal geometry and porosity were altered by Phospho1 deletion, compounded in Alpl^wt/Prx1;Phospho1^-/‒ mice, and linked to alterations in collagen configuration, matrix mineralization, and growth plate deformities. Together, our findings support a mechanistic framework for TNAP and PHOSPHO1 in permissive biomineralization, providing critical insights into this fundamental process.