Telomere DNA Content and Senescence of Dental Pulp

The telomeres of most human somatic cells shorten with successive cell division. The telomere length regulates the further cell division. Telomere shortening is a checkpoint signaling entry into senescence. Assessment of dental pulp senescence is useful to make decision in diagnosis and prognosis. Objectives: The purpose of this study was to establish a sensitive system that evaluates senescence of dental pulp by quantifying telomere DNA content (corresponding to telomere length). Methods: DNA was extracted from dental pulp that was obtained by pulpectomy. DNA was quantified with the fluorescent dye, using commercially available human genomic DNA as a standard. Sample DNA amounts were calculated from the equation describing the best-fit line generated with the standard DNA. Slot blots hybridization was performed using a commercially available Chemiluminescence kit. The intensity of telomere hybridization signal was determined from autoradiograph. Telomere DNA content was assayed by comparing the slope of the equation generated from DNA inputs versus the relative signal from genomic DNA at known concentration according to Dr. Jeffrey Griffith. Results: There was a linear relationship (R2=0.95~098) between telomere DNA content and inputs of 10-100 ng genomic DNA. The slopes for the telomere DNA contents of 23- and 26-year old patients were 79.9 and 73.8, respectively. In contrast, the slopes for those of 61- and 65-year old patients were 47.7 and 45.4, respectively. This was a kind of pilot study where the number of test samples was too small. Further studies are necessary to perform statistical analysis using more samples. Conclusion: We succeeded in quantifying telomere DNA content of dental pulp using as little as 10 ng genomic DNA. Telomere DNA content of dental pulp was nearly identical in the healthy donors of the same age and decreased by aging. Supported by a grant-in-aid of Ministry of Education, Science and Culture of Japan.