title: Phenotypic severity of autosomal dominant osteopetrosis type II (ADO2) mice on different genetic backgrounds recapitulates the features of human disease.
abstract: Autosomal dominant osteopetrosis type II (ADO2) is a heritable osteosclerotic bone disorder due to dysfunctional osteoclast activity. ADO2 is caused by missense mutations in the chloride channel 7 (CLCN7) gene characterized by osteosclerosis with multiple fractures. ADO2 can result in osteomyelitis, visual loss and bone marrow failure. Currently, there is no cure for ADO2, and until recently no appropriate animal model of ADO2 existed to understand better the pathogenesis of this disease and to test new therapies. Therefore, we created ADO2 knock-in mouse model with a G213R (human homolog of G215R) missense mutation in the Clcn7 gene on 129S1 background, and demonstrated that this mouse model phenocopies human ADO2. As ADO2 gives rise to incomplete penetrance (66%) in human and marked phenotypic variability is observed among patients with the same mutation, we hypothesized that the severity and penetrance of ADO2 will also vary in mouse models on different genetic backgrounds. To test this, we created ADO2 mouse models in DBA/D2, C57BL/6J/B6 and Balb/c strains, and compared bone phenotypes and performed serum biochemical analysis between strain- and age-matched wild-type (WT) and ADO2 mice. At 3months of age, whole body aBMD was higher (4-7% in male; 1-5% in female) in the ADO2 mice compared to their wild-type littermates. In addition, ADO2 male mice on 129 background displayed highest percent increase of BV/TV (106%), followed by D2 (92%), B6 (46%), and Balb/c (33%) compared to strain-matched wild-type mice. We observed similar differences for BV/TV between ADO2 and wild-type mice on different genetic backgrounds in female: 129 (96%)>D2 (73%)>Balb/c (39%) and B6 (36%). Serum calcium, phosphorus, alkaline phosphatase and P1NP levels were similar in the WT and ADO2 mice on all genetic backgrounds but TRAP was higher (76% to 220% in male; 33-95% in female) and CTX/TRAP ratio was lower (39-65% in male and 3-41% in female) in the ADO2 mice compared to their strain-matched wild-type littermates. We also found that young (3months) ADO2 mice on 129S1 background exhibited 200% higher trabecular BV/TV whereas old (18months) ADO2 mice displayed 400-700% higher BV/TV compared to their age-matched wild-type controls. In summary, phenotypic severity in ADO2 mice varied markedly on different genetic backgrounds (129>D2>Balb/c>B6) and became more pronounced with age, which resembles the wide variations in phenotype observed in ADO2 patients. These mouse models will help us to identify genes/factors that influence severity and penetrance of ADO2, and test innovative therapies to treat this disease.
authors.affiliation: Medicine, Indiana University School of Medicine, IN, USA. Electronic address: ialam@iu.edu.
authors.forename: Imranul
authors.initials: I
authors.lastname: Alam
authors.affiliation: Medicine, Indiana University School of Medicine, IN, USA.
authors.forename: Amie K
authors.initials: AK
authors.lastname: McQueen
authors.affiliation: Medicine, Indiana University School of Medicine, IN, USA.
authors.forename: Dena
authors.initials: D
authors.lastname: Acton
authors.affiliation: Medicine, Indiana University School of Medicine, IN, USA.
authors.forename: Austin M
authors.initials: AM
authors.lastname: Reilly
authors.affiliation: Medicine, Indiana University School of Medicine, IN, USA.
authors.forename: Rita L
authors.initials: RL
authors.lastname: Gerard-O'Riley
authors.affiliation: Medicine, Indiana University School of Medicine, IN, USA.
authors.forename: Dana K
authors.initials: DK
authors.lastname: Oakes
authors.affiliation: Medicine, Indiana University School of Medicine, IN, USA.
authors.forename: Charishma
authors.initials: C
authors.lastname: Kasipathi
authors.affiliation: Medicine, Indiana University School of Medicine, IN, USA.
authors.forename: Abigail
authors.initials: A
authors.lastname: Huffer
authors.affiliation: Medicine, Indiana University School of Medicine, IN, USA.
authors.forename: Weston B
authors.initials: WB
authors.lastname: Wright
authors.affiliation: Medicine, Indiana University School of Medicine, IN, USA; Medical and Molecular Genetics, Indiana University School of Medicine, IN, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Econs
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000097:blood; D001835:Body Weight; D015519:Bone Density; D001862:Bone Resorption / Q000097:blood / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology; D000071556:Cancellous Bone / Q000000981:diagnostic imaging / Q000473:pathology; D004195:Disease Models, Animal; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D008297:Male; D051379:Mice; D010022:Osteopetrosis / Q000097:blood / Q000150:complications / Q000235:genetics* / Q000473:pathology*; D010641:Phenotype; D055114:X-Ray Microtomography
chemical_list: D015415:Biomarkers
keywords: Bone mineral density; Genetic background; Osteoclast; Osteopetrosis; Phenotype