Both MMP-2 and MMP-9 (i.e., gelatinases A and B) have a broad spectrum
of degrading gelatin, basement membrane collagen, and elastin (see
reviews in
Refs. 7 and 9). Herein, we noted that the expression of
MMP-2 transcript and protein was unchanged, but that of MMP-9 was
specifically induced by TNF-α in normal conjunctival and
conjunctivochalasis fibroblasts. The latter finding was demonstrated by
gelatin zymography, ELISA, and Western blot analysis when experiments
were carried out for 24 hours, but not by Northern hybridization when
experiments were carried out for 5 hours, suggesting that protein
upregulation might take a longer time. No significant difference has
been noted between normal conjunctival fibroblasts and
conjunctivochalasis fibroblasts in the protein expression of MMP-9. In
human corneas, MMP-9 is not found in uninjured tissue but is
synthesized by cells of the repairing corneal epithelium and stroma
after injury.
30 Likewise, in rabbit corneas, MMP-9 is not
produced in normal tissue
31 but is found in corneal
epithelial and stromal layers after keratectomy.
32 To the
best of our knowledge, the expression of MMP-9 by HJFs has not been
reported. In this report, we noted that expression of MMP-9 by both HJF
and ChF was apparent only when TNF-α was added. A similar finding has
been reported in human endometrial stromal cells,
10 uterine cervical fibroblasts,
33 and dermal
fibroblasts.
34 Collectively, these data indicate that
TNF-α may play a unique role in MMP-9 expression by these mesenchymal
cells. It has been reported that upregulation of MMP-1 and MMP-3 genes
by phorbol ester and IL-1 may be via an AP-1 site.
7 Nevertheless, the MMP-9 gene comprises additional promoter sites for
NFκB and SP-1,
35 which may allow further
induction by TNF-α. For cultured keratinocytes, TNF-α–stimulated
MMP-9 and recombinant MMP-9 bind to the cell membrane, gelatin, and
type I and IV collagens.
36 This binding may cause the
delay in its clearance and may enhance matrix degradation in chronic
inflammation.
36 Moreover, enhanced production of MMP-9 has
been noted in human foreskin fibroblasts after treatment with basic
calcium phosphate crystals,
37 in human uterine cervical
fibroblasts after treatment with
12-
O-tetradecanoylphorbol,
33 in human dermal
skin fibroblasts after UV radiation,
38 in corneal stroma
after surgical trauma,
30 and in granulation tissue of oral
mucosa wounds.
39 Therefore, we speculate that matrix
degradation in conjunctivochalasis may be further promoted when TNF-α
is produced.