Induction of a NOTCH3 Lehman syndrome mutation in osteocytes causes osteopenia in male C57BL/6J mice

Lateral Meningocele or Lehman Syndrome (LMS) is associated with NOTCH3 mutations causing deletions of the PEST domain and a gain-of-NOTCH3 function. We demonstrated that Notch3 mice harboring Notch3 mutations analogous to those found in LMS are osteopenic because of enhanced bone resorption. To determine the contribution of specific cell lineages to the phenotype, we created a conditional-by-inversion (Notch3 ) model termed Notch3 in which Cre recombination generates a Notch3 allele expressing a NOTCH3 mutant lacking the PEST domain. Germ line Notch3 inversion caused osteopenia and phenocopied the Notch3 mutant, validating the model. To induce the mutation in osteocytes, smooth muscle and endothelial cells, Notch3 mice were bred with mice expressing Cre from the Dmp1, Sm22a and Cdh5 promoters, respectively, creating experimental mice harboring Notch3 alleles in Cre-expressing cells and control littermates harboring Notch3 alleles. Notch3 inversion in osteocytes led to femoral and vertebral cancellous bone osteopenia, whereas Notch3 inversion in mural Sm22a or endothelial Cdh5-expressing cells did not result in a skeletal phenotype. In conclusion, introduction of the LMS mutation in osteocytes but not in vascular cells causes osteopenia and phenocopies Notch3 global mutant mice.