KGF

Function of Keratinocyte Growth Factor (KGF) During Chronic Inflammation

BACKGROUND
Significant epithelial cell proliferation is associated with the chronic inflammatory conditions, Periodontitis. Regulation of this proliferation is poorly understood but most likely is controlled by locally expressed growth factors. Although a variety of growth factors may be involved in regulating this process our laboratory has focused its work on a specific group of epithelial-specific growth factors. These are designated as Keratinocyte Growth Factors-1 (FGF-7) and -2 (FGF-10). For further information the reader is referred to a review (Putnins 2001). Keratinocyte Growth Factors are members of the ever-growing family of Fibroblast Growth Factors (FGF). They are unique within this family because they are designated as paracrine mediating epithelial cell-specific growth factors. That is, KGFs are expressed by fibroblasts and only epithelial cells express the appropriate KGF-specific receptor (FGFR2-iiib). From a functional perspective KGF-1 is a potent inducer of keratinocyte proliferation. In addition we have shown in conjunction with others that KGF-1 induced keratinocyte migration but migration was dependant on specific types of extracellular matrix proteins that were present (Putnins et al., 1999). Expression of KGF is significantly increased during wound healing and therefore may regulate the proliferation and migration of wound edge epithelial cells. Since progression of periodontal disease can be described as attempted healing in a site with a chronic inflammatory challenge we elected to examine the role that KGFs may play during periodontal disease.

PROJECT PROGRESS:

1) Regulation and expression of KGF-1 and -2 by gingival fibroblasts.
Our laboratory was the first to examine the regulation of expression of KGF-1 and -2 protein and gene expression in gingival fibroblasts. We have established that gingival fibroblasts do express KGF-1 and -2 gene transcripts but only KGF-1 protein and gene expression was induced by the addition of serum and proinflammatory cytokines (Sanaie et al., 2002). These data suggest that KGF-1 may play a very significant role in chronic inflammation (i.e. periodontitis). Support for this hypothesis is found in other nonoral studies which have shown that KGF is also upregulated in other chronic inflammatory disorders (i.e. Crohn’s disease, ulcerative colitis and psoriasis). The in vivo role of KGF during onset and progression of periodontal disease is as yet unclear but is a one of the current focuses of the laboratory.

2) Lipopolysaccharide (LPS) induces KGF-1 gene and protein expression.
Our laboratory was the first to show that LPS is a potent inducer of KGF-1 expression (Putnins et al. 2002). LPS induction of KGF-1 protein expression was dependent on gingival fibroblast expression of membrane associated CD14, Toll-like receptors 2 and 4. Lipopolysaccharide induced low mCD14 expressing gingival fibroblasts to express mCD14 at a level that was consistent with high mCD14 expressing cells. Functional studies using specific blocking antibodies for CD14 and Toll-like receptors 2 and -4 implicated all of these molecules in the signaling cascade. LPS is one member of a group of molecules called pathogen associated molecular pattern (PAMPs) molecules that are recognized by host tissues that express pattern recognition receptors (PRRs). Recognition of microorganisms by this mechanism forms part of the primitive form of defense called innate immunity. However, we showed LPS regulation of KGF-1 expression is also regulated through this pathway. It is interesting to speculate on the clinical significance of this finding. During the progression of periodontal disease the epithelial cell barrier can be disrupted allowing LPS to directly stimulate gingival fibroblasts to express KGF-1. Expression of KGF-1 and subsequent specific stimulation of epithelial cell proliferation may ultimately serve to reestablish and maintain an effective epithelial cell barrier. Establishment and maintenance of an epithelial barrier is one key aspect of innate immunity [see review-Dale BA (2002) Perio 2000, 30:70-78]. This in turn may protect the host from periodontal disease associated Gram-negative pathogens in dental plaque biofilm.

3) KGF-1 Expression in Periodontal Tissues
Keratinocyte Growth Factor-1 (KGF-1) is upregulated in chronic inflammation and specifically stimulates epithelial cell proliferation by signaling through the epithelial-specific Keratinocyte Growth Factor Receptor (KGFR). We examined KGF-1 and KGFR protein and gene expression in healthy and diseased periodontal tissues. Tissues were collected from patients with periodontal health or disease, immediately frozen and stained for KGF and KGFR protein expression. Laser capture microdissection of epithelial and connective tissue cells with RT-PCR examined KGF-1 and KGFR gene expression profiles and enzymatic digestion with heparitinase, chondroitinase ABC or pretreatment with suramin examined epithelial surface molecule interactions with KGF-1. In tissues collected from healthy patients, KGF-1 protein localized to areas of junctional and basal oral epithelial cells and was significantly increased in periodontal pocket epithelium and in the oral epithelium of disease-associated tissues. KGFR localized to the junctional and the parabasal cells of oral epithelium, with the relative staining intensity being increased in disease-associated pocket epithelium. Laser capture microdissection with RT-PCR confirmed KGF and KGFR were specifically expressed by connective tissue and epithelium, respectively. KGF-1 and KGFR proteins are expressed in health but significantly increased in diseased periodontal tissues. We hypothesize that the upregulation of KGF-1 and KGFR protein associated with disease regulates epithelial cell behavior associated with onset and progression of periodontal pocket formation (Li., et al., 2004-manuscript submitted).

INVESTIGATORS

Visiting Scientists and Research Associates

  • Jim Firth

Post Docs

  • Daisuke Ekuni, (April 2004-05)
    Okayama University Hospital,
    Okayama, JAPAN

Graduate Students

  • Yi Yang (2003-_____ Ph.D.)
  • Min Li (2001-_____ Ph.D.)
  • Tassos Irinakis (1999-2003 M.Sc)
  • Nazanin Narani (1998-2000 M.Sc)
  • Ali-Reza Sanaie (1998-2000 M.Sc)
  • Laura Noce (1996-1998 M.Sc)

Laboratory Technicians