Ameloblastin is not implicated in bone remodelling and repair

Abstract

Ameloblastin (AMBN) is an enamel matrix protein produced by ameloblasts. It has been suggested that AMBN might also be implicated in craniofacial bone formation. Our objective was to determine whether AMBN has an effect on osteogenic mineralisation and infl uences bone remodelling and repair. MC3T3-E1 cells were screened for endogenous expression of enamel proteins using real time PCR. Various osteogenic cells were infected with lentivirus encoding for AMBN and protein expression was verifi ed using immunochemistry. Cultures were stained with alizarin red and mineralisation was quantifi ed. Healing bone was probed for expression of AMBN by DNA microarray analysis. Tooth extraction, experimental tooth movement (ETM), and creation of a non-critical size bone defect in the tibia (BDT) were carried out in wild type and AMBN Δ5-6 mutant mice. Tissues were processed for immunolabelling of AMBN and Bril, an osteoblast specifi c protein associated with active bone formation. MC3T3-E1 cells and healing bone showed no significant expression of AMBN. Overexpression of AMBN in osteogenic cultures induced no noticeable changes in mineralisation. In wild type mice, AMBN was immunodetected in ameloblasts and enamel, but not in normal bone, and at sites where bone remodelling and repair were induced. Bone remodelling during ETM and BDT repair in AMBN Δ5-6 mice were not signifi cantly different from that in wild type animals. Our results suggest that AMBN does not infl uence osteogenic activity in vitro under the conditions used, and does not participate in craniofacial bone remodelling under mechanical stress and in repair of non-critical size bone defects.

The ameloblastin extracellular matrix molecule enhances bone fracture resistance and promotes rapid bone fracture healing

“…AMBN might have three functions in this process, (i) to provide additional templating sites for bone mineralization, (ii) to enhance cell adhesion as a requirement for mineralized tissue formation, and (iii) to modulate osteogenic signaling via BMPs, Runx2 and Osx. Differences between our findings indicating that loss of AMBN function results in delayed bone fracture healing and a previous report (39) are likely due to differences in data interpretation and analysis techniques.…”

Tracking Endogenous Amelogenin and Ameloblastin In Vivo

“…5). Indeed, distinct dysmorphologies characterize bones in which AMELX [16], [49] or AMBN [24], [50] expression are genetically modified, even though calcium and phosphorus content and the degree of mineralization are normal [51], [52]. Disturbed EMP expression patterns are associated with alveolar and jaw bone malformations [33], [34].…”

Evolutionary analysis of selective constraints identifies ameloblastin (AMBN) as a potential candidate for amelogenesis imperfecta

“…It is worth noting that (i) AMBN expression was reported during craniofacial bone development in rats [ 35 ], and (ii) in vitro and in vivo experiments have suggested that this protein could also play a role in bone formation and repair [ 27 , 36 , 37 ]. These findings could indicate that AMBN plays a role in early bone formation and modeling, but they have been contradicted by a study showing no implication in bone modeling and repair [ 38 ]. Moreover, a possible function in bone development remains elusive as (i) AMBN −/− mice do not exhibit apparent bone phenotype [ 21 ], (ii) AMBN is subjected to pseudogenization in birds and in mammalian species, in which the capability to form either enamel or teeth has been lost, e.g., xenarthrans, pangolins and baleen whales, indicating that AMBN is a tooth specific protein [ 39 – 41 ], and (iii) AMBN expression was found to be restricted to teeth in rodents and in a crocodile [ 9 , 14 ].…”