Differential distribution of lumican and fibromodulin in tooth cementum

The objectives of this study were to isolate and characterize the major proteoglycans of tooth cementum in relation to the tissue's mineralization. Cementum was collected from the root apex region of bovine molars and pulverized. It was first extracted with 6M guanidine-HCI, pH 7.4 (G-extract, mineral-unassociated) and then demineralized and extracted with 0.5M EDTA (E-extract, mineral-associated). Both extracts were applied to anion exchange and then molecular sieve chromatography to isolate proteoglycans. The fractions collected were assayed for chondroitin-(CS) and keratan sulfate (KS) containing proteoglycans using the monoclonal antibodies 2-B-6 and 5-D-4, respectively. It was found that the KS was the major glycosaminoglycan and was enriched in the G-extract fraction. The major KS fraction was then applied to 7.5% SDS-PAGE. The major broad band (69 kDa) was 5-D-4 positive in Western blot analysis and separated into two bands (46 kDa and 50 kDa) after treatment with keratanase II and endo-beta-galactosidase. These two proteins were transfered to PVDF membrane and analyzed for amino acid sequence. The results showed the major band (46 kDa) to be lumican and the minor (50 kDa) fibromodulin. In addition, based on the immunohistochemical study using a number of mono- and polyclonal antibodies including 5-D-4, anti-lumican core protein as well as anti-fibromodulin core protein antibodies, the KSPGs were found to be located almost exclusively in nonmineralized portions of cementum such as precementum and the pericementocyte area. These biochemical as well as immunohistochemical data suggest that the major KSPGs of cementum, lumican and fibromodulin, have a specific tissue distribution and may have regulatory roles in cementum mineralization.