Type VII collagen is enriched in the enamel organic matrix associated with the dentin–enamel junction of mature human teeth

Abstract

The inner enamel region of erupted teeth is known to exhibit higher fracture toughness and crack growth resistance than bulk phase enamel. However, an explanation for this behavior has been hampered by the lack of compositional information for the residual enamel organic matrix. Since enamel-forming ameloblasts are known to express type VII collagen and type VII collagen null mice display abnormal amelogenesis, the aim of this study was to determine whether type VII collagen is a component of the enamel organic matrix at the dentin-enamel junction (DEJ) of mature human teeth. Immunofluorescent confocal microscopy of demineralized tooth sections localized type VII collagen to the organic matrix surrounding individual enamel rods near the DEJ. Morphologically, immunoreactive type VII collagen helical-bundles resembled the gnarled-pattern of enamel rods detected by Coomassie Blue staining. Western blotting of whole crown or enamel matrix extracts also identified characteristic Mr=280 and 230 kDa type VII dimeric forms, which resolved into 75 and 25 kDa bands upon reduction. As expected, the collagenous domain of type VII collagen was resistant to pepsin digestion, but was susceptible to purified bacterial collagenase. These results demonstrate the inner enamel organic matrix in mature teeth contains macromolecular type VII collagen. Based on its physical association with the DEJ and its well-appreciated capacity to complex with other collagens, we hypothesize that enamel embedded type VII collagen fibrils may contribute not only to the structural resilience of enamel, but may also play a role in bonding enamel to dentin.

Type IV Collagen is a Novel DEJ Biomarker that is Reduced by Radiotherapy

“…We hypothesize that localization of both types IV and VII collagen (McGuire et al, 2014b) to this region could help explain these previously reported properties of the DEJ. By analogy with the mechanical stability of the dermal-epidermal junction in skin Immunoreactivity of type IV collagen was greatly diminished in both the cuspal and cervical regions after 6 hr of digestion with purified bacterial collagenase.…”

“…Extraction of enamel matrix proteins from additional thirdmolar tooth crowns (n = 6) was accomplished by complete decalcification of each crown, enamel surface up, for 14 days in 40 mL of 10% EDTA (7.4 pH) containing 0.002% NaN 3 at 20°C (McGuire et al, 2014b). The enamel organic matrix layer was then recovered by gentle wiping of the dentin surface with a ballpoint-applicator microbrush (Kerr Totalcare, Orange, CA, USA).…”

“…Based on a possible developmental relationship with the dental BM, we recently identified that type VII collagen surrounds the enamel rods as a component of the enamel organic matrix (McGuire et al, 2014b). Since types VII and collagen IV are generally co-localized in basement membranes and form functional complexes (Timpl, 1989), and since the DEJ represents the original position of the dental BM (Imbeni et al, 2005), we asked whether type IV collagen was a component of this interfacial region in mature teeth, and whether it was affected in teeth exposed to high-dose radiotherapy.…”

“…These findings suggest a radiogenic effect on tooth structure with increasing radiation dose to the tooth. To better understand radiotherapy-induced DEJ instability leading to dentition breakdown, our group is focused on characterizing the structure, properties, and biochemical composition (Dusevich et al, 2012;Xu et al, 2012;McGuire et al, 2014b) of the DEJ, as well as postradiation changes (McGuire et al, 2014a).…”

Morphology of Organic Matrix of Human Enamel

“…1 a, b). There is a strong indication that these are fibers of type VII collagen which can complex with other collagens and may contribute to the structural resilience of enamel and play a role in bonding enamel to dentin [4].Crystals of hydroxyapatite in human enamel are long but narrow (20-80 nm in cross section); they are organized in parallel bundles, so called "enamel rods," of about 4-8 microns in diameter. Morphologically organic matrix is following the shape of these rods.…”