Introduction of a Phe377del Mutation in ANK Creates a Mouse Model for Craniometaphyseal Dysplasia

Abstract

Craniometaphyseal dysplasia (CMD) is a monogenic human disorder characterized by thickening of craniofacial bones and flaring metaphyses of long bones. Mutations for autosomal dominant CMD have been identified in the progressive ankylosis gene ANKH. Previous studies of Ank loss-of-function models, Ank null/null and Ank ank/ank mice, suggest that Ank plays a role in the regulation of bone mineralization. However, the mechanism for Ank mutations leading to CMD remains unknown. We generated the first knockin (KI) mouse model for CMD expressing a human mutation (Phe377 deletion) in ANK. Homozygous Ank knockin mice (Ank KI/KI ) replicate many typical features of human CMD including hyperostosis of craniofacial bones, massive jawbones, decreased diameters of cranial foramina, obliteration of nasal sinuses, fusion of middle ear bones, and club-shaped femurs. In addition, Ank KI/KI mice have increased serum alkaline phosphatase and TRACP5b, as reported in CMD patients. Biochemical markers of bone formation and bone resorption, N-terminal propeptide of type I procollagen and type I collagen cross-linked C-terminal telopeptide, are significantly increased in Ank KI/KI mice, suggesting increased bone turnover. Interestingly, Ank KI/KI bone marrow-derived macrophage cultures show decreased osteoclastogenesis. Despite the hyperostotic phenotype, bone matrix in Ank KI/KI mice is hypomineralized and less mature, indicating that biomechanical properties of bones may be compromised by the Ank mutation. We believe this new mouse model will facilitate studies of skeletal abnormalities in CMD at cellular and molecular levels.

Autosomal Recessive Mental Retardation, Deafness, Ankylosis, and Mild Hypophosphatemia Associated with a NovelANKHMutation in a Consanguineous Family

“…This finding is currently explained by accelerated bone resorption in long bones rather than the calvaria (32,33). This is supported by increased osteoclast numbers per trabecular bone surface in ank long bones (32).…”

“…This finding is currently explained by accelerated bone resorption in long bones rather than the calvaria (32,33). This is supported by increased osteoclast numbers per trabecular bone surface in ank long bones (32). In patients affected by ankylosing spondylitis and corresponding animal models, osteopenia as a consequence of joint destruction has been well established (1,34).…”

Increased trabecular bone formation in mice lacking the growth factor midkine

“…(40,41,52) Moreover, the recent analysis of a mouse model of craniometaphyseal dysplasia has further revealed high bone turnover, thereby suggesting that at least the inactivation of Ank can result in an activation of bone resorption. (53) Although these findings raise the possibility that Ank and Enpp1 are downstream effectors of Mdk in the regulation of bone formation, it is important to state that we cannot rule out that Mdk influences bone remodeling through other mechanisms. For instance, Mdk has been shown to promote the migration of inflammatory leukocytes and the differentiation of osteoclasts from macrophages, thereby explaining its potential relevance in rheumatoid arthritis.…”

The Progressive Ankylosis Protein Regulates Cementum Apposition and Extracellular Matrix Composition

“…In a dental case report on a young CMD patient, we described ectopic mineral on maxillary molars which was not inconsistent with the mineral accumulation in Ank KO mice teeth [Zhang et al, 2007]. A mouse model phenocopying CMD was successfully created by knocking in the human ANKH mutation responsible for CMD, though tooth development was not detailed [Chen et al, 2009]. Additionally, a novel ANKH mutation has recently been identified in 6 patients from a family of Turkish ethnicity, all featuring joint pain and restricted movement similar to Ank mutant and KO mice [Morava et al, 2010].…”