Characteristic genes expressed in periodontal ligament

Objectives: For understanding the intrinsic functions and the physiological and pathological conditions of periodontal ligament (PDL), a comprehensive understanding of molecules expressed in PDL is a prerequisite. Therefore, this study was focused on the clarification of genes preferentially expressed in adult human PDL. Methods: Suppression subtractive hybridization is very effective to enrich differentially expressed genes in two different tissues or cells. We therefore used the technique to identify characteristic molecules expressed in adult human PDL tissue as compared to PDL-derived dedifferentiated cells. Total RNA was extracted from each tissue or cell, and subtracted cDNA libraries were constructed. A total of 420 clones were randomly isolated from a PDL cDNA library and their cDNA sequences were compared with sequences in GenBank database. Unique genes were further characterized by RT-PCR, Northern blot, Western blot, and in situ hybridization analyses. Results: The most enriched genes in a subtracted PDL cDNA library are type I and type III collagens that are the main constituents of the extracellular matrix (ECM) of PDL. The third gene is nasopharyngeal carcinoma-associated peptide (NAP-1) whose expression has never been reported in PDL. NAP-1 is a small secreted peptide and has been suggested to have a possible role in immunomodulation. However, further work will be necessary to clarify its function in PDL. Other enriched genes, such as lumican, periostin, PLAP-1 and so on are mostly ECM components, whose expressions in PDL would provide unique properties to the tissue. Conclusion: We revealed that several characteristic genes including NAP-1 were preferentially expressed in PDL tissue. Our findings will provide a new view of PDL tissue.