Enamelysin (Matrix Metalloproteinase 20)-deficient Mice Display an Amelogenesis Imperfecta Phenotype

Abstract

Enamelysin is a tooth-specific matrix metalloproteinase that is expressed during the early through middle stages of enamel development. The enamel matrix proteins amelogenin, ameloblastin, and enamelin are also expressed during this same approximate developmental time period, suggesting that enamelysin may play a role in their hydrolysis. In support of this interpretation, recombinant enamelysin was previously demonstrated to cleave recombinant amelogenin at virtually all of the precise sites known to occur in vivo. Thus, enamelysin is likely an important amelogenin-processing enzyme. To characterize the in vivo biological role of enamelysin during tooth development, we generated an enamelysindeficient mouse by gene targeting. Although mice heterozygous for the mutation have no apparent phenotype, the enamelysin null mouse has a severe and profound tooth phenotype. Specifically, the null mouse does not process amelogenin properly, possesses an altered enamel matrix and rod pattern, has hypoplastic enamel that delaminates from the dentin, and has a deteriorating enamel organ morphology as development progresses. Our findings demonstrate that enamelysin activity is essential for proper enamel development.Dental enamel covers the crown of the tooth and is unique among mineralized tissues because of its high mineral content, large crystals, and organized prism pattern. Other mineralized tissues such as bone, dentin, and cementum are composed of ϳ20% organic material. In contrast, mature enamel has less than 1% organic matter by weight (1, 2). Moreover, enamel crystallites possess a volume that is 100 times greater than the volume of crystallites found in other mineralizing tissues. These enamel crystallites form enamel rods that, in turn, form a unique interlacing (decussating) prism pattern. As a result, dental enamel is the hardest substance in the body. Its hardness is intermediate between that of iron and carbon steel, yet it also has a high elasticity (3).Although mature enamel is a very hard protein-free tissue, it does not start this way. Enamel development (amelogenesis) consists of several stages that include the secretory, transition, and maturation stages. During the secretory stage, enamel crystallites elongate into long thin ribbons that are only a few apatitic unit cells in thickness (about 10 nm) with a width of ϳ30 nm (4, 5). The ribbons are evenly spaced, are oriented parallel to each other, and grow in length but very little in width and thickness. Ultimately, enamel crystal length determines the final thickness of the enamel layer as a whole (for review, see Ref. 6). It is during the secretory stage that the columnar-shaped ameloblast cells, located adjacent to the forming enamel, secrete specialized enamel proteins into the enamel matrix. These proteins include amelogenin (7), ameloblastin (8), and enamelin (9). Amelogenin is the predominant component and comprises ϳ90% of total enamel matrix protein (10). Interestingly, the full-length enamel proteins are found only at the mineralizing front, su...

Functions of KLK4 and MMP-20 in dental enamel formation

“…Insights into the function of MMP-20 in enamel formation have been gained by the characterization of MMP-20 null mice Caterina et al, 2002). In the absence of MMP-20 activity, failure to digest the matrix prevents the thickening of secretory stage crystals in the deeper enamel.…”

MT1‐MMP: A tethered collagenase

“…MMP-20 is unique among MMPs as its expression is restricted to ameloblasts and odontoblasts of developing teeth. Mice deficient in MMP-20 display a severe and progressive enamel defect reminiscent of human amelogenesis imperfecta (Caterina et al, 2002). MMP-20 cleaves amelogenin in vitro.…”

FAM20C Plays an Essential Role in the Formation of Murine Teeth

“…The amelogenesis process is divided into the presecretory stage, secretory stage, and maturation stage, with marker genes expressed at each phase. Over the past decade, mouse models engineered for the loss-of-function analyses of AMEL (29), AMBN (30,31), ENAM (32), MMP20 (33), and KLK4 (34) have been reported. Among these engineered models, the enamel defects of Ambn KO and Enam KO mice (35) were very similar to those of the Fam20C KO mice.…”