Smpd3 Expression in both Chondrocytes and Osteoblasts Is Required for Normal Endochondral Bone Development

Abstract

Sphingomyelin phosphodiesterase 3 (SMPD3), a lipid-metabolizing enzyme present in bone and cartilage, has been identified to be a key regulator of skeletal development. A homozygous loss-of-function mutation called fragilitas ossium (fro) in the Smpd3 gene causes poor bone and cartilage mineralization resulting in severe congenital skeletal deformities. Here we show that Smpd3 expression in ATDC5 chondrogenic cells is downregulated by parathyroid hormone-related peptide through transcription factor SOX9. Furthermore, we show that transgenic expression of Smpd3 in the chondrocytes of fro/fro mice corrects the cartilage but not the bone abnormalities. Additionally, we report the generation of Smpd3^flox/flox mice for the tissue-specific inactivation of Smpd3 using the Cre-loxP system. We found that the skeletal phenotype in Smpd3^flox/flox; Osx-Cre mice, in which the Smpd3 gene is ablated in both late-stage chondrocytes and osteoblasts, closely mimics the skeletal phenotype in fro/fro mice. On the other hand, Smpd3^flox/flox; Col2a1-Cre mice, in which the Smpd3 gene is knocked out in chondrocytes only, recapitulate the fro/fro mouse cartilage phenotype. This work demonstrates that Smpd3 expression in both chondrocytes and osteoblasts is required for normal endochondral bone development.

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.01077-15.

ACKNOWLEDGMENTS

We declare no conflict of interest.

We thank Mia Esser and Louise Marineau for animal husbandry, Marie-Helene Gaumond for technical support, Anujan Gunaratnam for generating a luciferase construct, and Veronique Lefebvre for providing the aggrecan promoter construct.

The core facility for skeletal phenotyping was supported by Le Réseau de Recherche en Santé Buccodentaire et Osseuse (RSBO). This work was supported by operating grants from the Canadian Institutes of Health Research (CIHR) Fund (number 123310 to M.M.). M.M. is an FRQS chercheur-boursier. P.M. is supported by the Shriners of North America. G.M. receives a studentship from the McGill University Health Center.