Lysophosphatidic acid regulates human gingival and periodontal ligament fibroblast expression of PDGF receptors

Abstract

LPA, a G protein‐coupled lipid mediator involved in wound healing, binds to LPA1‐5 receptors (LPARs). It is co‐released by activated platelets together with platelet‐derived growth factor (PDGF). We have published that human gingival (GF) and periodontal ligament (PDLF) fibroblasts express LPA1‐3, and that LPA positively regulates their responses to PDGF. In this study, we tested the hypotheses that LPA exerts these effects in part by 1) transactivating the PDGFR‐ β, and 2) regulating plasma membrane expression of PDGF receptors. Using immunoprecipitation and Western blotting (IP/WB), antibodies specific for the activated form of the PDGFR‐ β were used to detect if stimulation with LPA transactivates this receptor. Determination of cell‐surface expression of PDGFRs was done by flow cytometry with antibodies specific for PDGFR‐α and ‐ β. Serum‐starved cells in 100‐mm dishes were stimulated with 1 x 10−7 ‐ 1 x 10−5M LPA for 0, 2, 4, and 6h, and the levels of PDGFR ‐α and ‐ β were measured. We were not able to detect transactivation of the PDGFR‐ β in GF or PDLF by IP/WB. However, LPA modulates the cell‐surface expression of both PDGFR‐α and ‐ β, consistently increasing the number of PDGFR‐α and ‐ β‐positive cells between 2‐12‐fold (in a donor‐dependent fashion, compared to untreated controls), between 2 and 4h post‐LPA treatment. From these results, we conclude that the PDGFR‐ β is not transactivated by LPA in GF and PDLF, but that LPA does exert complex regulation of both PDGFR‐α and ‐βin these cells. Support: NIH/NIDCR 1 R15 DE016855‐03 (D.R.C).