Action of metalloproteinases on porcine dentin mineralization

Samples containing predentin and mineralized dentin involving the mineralized front (newly formed dentin) were prepared by scraping developing porcine teeth after odontoblastic cell debris had been removed from the predentin surfaces. An extract was obtained separately from the matrices of predentin and of the newly formed dentin with a 4 M guanidine solution before and after demineralization with acetic acid solution. Enzymography detected 56 and 61 kDa gelatinases and 25 kDa proteoglycanase as neutral metalloproteinases in both extracts and proved them to be in an active form. Approximately half of the 56 and 61 kDa gelatinases binds to collagen fibers in predentin matrix. Three high molecular weight proteoglycans (70-85 kDa, 130-180 kDa, and 290 kDa) were found in the predentin matrix, but not in the newly formed dentin. The proteoglycanases in predentin degraded 290 kDa proteoglycan, if incubated together with calcium (Ca) ions. The results of this investigation indicate that active proteoglycanases which existed in the predentin perform no substantial work in proteoglycan degradation because the Ca ions are masked in the predentin matrix by coexisting proteoglycans. When mineralization occurs, however, they can degrade the proteoglycan at the mineralization front because excess Ca ions may be supplied via odontoblastic processes.