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Regulation
of Lysyl Oxidase, Collagen, and Connective Tissue Growth Factor by TGF-[beta]1
and Detection in Human Gingiva |
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Hsiang-Hsi Hong,
Mehmet Ilhan Uzel, Chunni Duan, Michael C. Sheff, and Philip C. Trackman |
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Division
of Oral Biology (H-HH, MIU, CD, PCT), Boston University School of Dental
Medicine, Department of Biochemistry (PCT), Boston University School of
Medicine, and Department of Pediatric Dentistry (MCS), Boston University
School of Dental Medicine and Franciscan Children's Hospital and Rehabilitation
Center, Boston, Massachusetts |
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SUMMARY: Gingival overgrowth
is characterized by excess extracellular matrix accumulation and elevated
levels of cytokines, including transforming growth factor-[beta]1 (TGF-[beta]1).
The functional relationships between altered cytokine levels and extracellular
matrix accumulation have not been extensively investigated in gingival cells
and tissues. Lysyl oxidase catalyzes the final known enzymatic step required
for cross-linking collagen and elastin in the synthesis of a functional
extracellular matrix. This study investigated the regulation by TGF-[beta]1
of lysyl oxidase and its collagen and elastin substrates in early passage
human gingival fibroblasts. In addition, TGF-[beta]1 regulation of connective
tissue growth factor (CTGF) was assessed in human gingival cells and tissues.
The results show that TGF-[beta]1 increases lysyl oxidase enzyme activity
and mRNA levels for lysyl oxidase and [alpha]-1-type I collagen, but not
elastin, in a dose- and time-dependent manner. Maximal stimulation of lysyl
oxidase activity and mRNA levels for both lysyl oxidase and collagen occurs
after 48 hours of treatment of gingival fibroblastic cells with 400 pm of
TGF-[beta]1. This study shows for the first time that CTGF mRNA and protein
are strongly and rapidly induced by TGF-[beta]1 in human gingival fibroblasts.
Exogenous addition of 1 to 50 ng/ml CTGF to gingival fibroblasts stimulates
production of lysyl oxidase enzyme activity up to 1.5-fold after 48 hours,
and 50 ng/ml CTGF stimulated insoluble collagen accumulation 1.5- to 2.0-fold
after 4, 11, and 18 days of treatment. It is interesting to note that the
addition of CTGF-blocking antibodies in the presence of TGF-[beta] did not
block TGF-[beta] stimulation of collagen mRNA levels. Thus, although CTGF
itself contributes to increased insoluble collagenous extracellular matrix
accumulation, CTGF does not mediate all of the effects of TGF-[beta]1 on
stimulation of collagen mRNA levels in human gingival fibroblasts. Immunohistochemistry
studies of gingival overgrowth tissue samples indicate for the first time
detectable levels of CTGF protein in Dilantin-induced hyperplasia tissues
also positive for TGF-[beta]1. CTGF was not found in TGF-[beta]1-negative
samples. In addition, extracellular lysyl oxidase protein was detected in
vivo. Taken together, these studies support mostly independent roles for
TGF-[beta]1 and CTGF in stimulating collagenous extracellular matrix accumulation
in human gingival fibroblasts and tissues. |
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