A Hepatocyte Growth Factor (HGF)/receptor autocrine loop regulates constitutive self-renewal of human periodontal ligament cells but reduces sensitivity to exogenous HGF.
BACKGROUND
In addition to its prominent role in liver regeneration, hepatocyte growth factor (HGF) is now generally thought to be produced by mesenchymal cells to promote the regeneration of epithelial tissue by a paracrine mechanism. However, it is not known how or if HGF could be involved in the regeneration of periodontal tissues. The purpose of this study was to characterize the ability of normal human periodontal ligament (PDL) cells to produce or respond to HGF.


METHODS
PDL cells derived from healthy young volunteers were used from passages four through 10. HGF receptors were detected both by immunocytochemical staining and Western-blotting analysis. Both DNA synthesis (by bromo-deoxyuridine [BrdU]-incorporation) and secreted HGF were quantified by enzyme-linked immunosorbent assays. Mitogen-activated protein kinase (MAPK) phosphorylation was also analyzed by Western blot.


RESULTS
Despite the immunocytochemical demonstration of HGF receptor protein in the cytoplasm and on the plasma membrane of PDL cells, exogenous recombinant human HGF did not exert the mitogenic effects expected. As reported for other mesenchymal cells, PDL cells were found to secrete HGF. Treatments with neutralizing anti-HGF antibody significantly suppressed constitutive PDL cell proliferation and sustained the receptor protein at higher levels than in non-treated cells. Under these conditions, exogenous HGF rapidly phosphorylated extracellular signal-regulated kinase (ERK), an action linked to the cell proliferation and downregulation of cell-surface receptors.


CONCLUSIONS
Unlike other known mesenchymal or epithelial cells, these findings suggest that normal PDL cells from young donors possess a constitutive HGF/receptor autocrine loop that normally regulates their replacement self-proliferation but reduces sensitivity to exogenously applied HGF by acute receptor downregulation.
Kawase
Tomoyuki
T
Division of Oral Regeneration and Transplantation Research, Department of Tissue Regeneration and Reconstruction, Institute of Medicine and Dentistry, Niigata University, Niigata, Japan. kawase@dent.niigata-u.ac.jp
Okuda
Kazuhiro
K
Yoshie
Hiromasa
H
D000293:Adolescent; D019898:Autocrine Communication / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000737:chemistry; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D002648:Child; D003593:Cytoplasm / Q000737:chemistry; D004247:DNA / Q000096:biosynthesis; D015536:Down-Regulation; D005260:Female; D017228:Hepatocyte Growth Factor / Q000032:analysis / Q000494:pharmacology / Q000502:physiology*; D006801:Humans; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000032:analysis; D008934:Mitogens / Q000494:pharmacology; D010513:Periodontal Ligament / Q000166:cytology* / Q000502:physiology; D010766:Phosphorylation; D019859:Proto-Oncogene Proteins c-met / Q000032:analysis / Q000187:drug effects / Q000502:physiology*
D008934:Mitogens; D017228:Hepatocyte Growth Factor; D004247:DNA; D019859:Proto-Oncogene Proteins c-met; D020928:Mitogen-Activated Protein Kinases