Transforming growth factor-beta 1 and -beta 2 positively regulate TGF-beta 1 mRNA expression in trabecular cells.

PURPOSE

To determine whether transforming growth factor (TGF)-beta 1 and -beta 2 and basic fibroblast growth factor (bFGF) induce the gene expression of TGF-beta 1 in the first-passage trabecular meshwork cells of the eye.

METHODS

Trabecular meshwork cells were cultured from fresh porcine eyes and treated with 1 ng/ml of TGF-beta 1, TGF-beta 2, or bFGF for 1 hour. Cells maintained in serum-free medium were used as controls. Total cellular RNA was extracted, and the first-strand cDNA was synthesized. Multiplex polymerase chain reaction (PCR) and competitive PCR were performed on aliquots of the cDNAs by using either endogenous (glyceraldehyde-3-phosphate dehydrogenase [G3PDH]) or exogenous sequence (PCR mimic for TGF-beta 1) as internal standards, respectively. The obtained products were quantitated by laser densitometry, and statistical analysis was performed.

RESULTS

The findings show that trabecular cells in vitro express the TGF-beta 1 messenger RNA constitutively. Both the techniques of multiplex PCR and competitive PCR demonstrated that the addition of either TGF-beta 1 or TGF-beta 2 at a concentration present in normal aqueous humor increased the mRNA levels of TGF-beta 1 by 2.82-to 3.07-fold over the controls, and these results were statistically significant (P < 0.01). Basic fibroblast growth factor did not have an effect on TGF-beta 1 expression (P < 0.05).

CONCLUSIONS

Transforming growth factor-beta 1 activates its own gene expression in trabecular cells. Considering the multifunctional property of this cytokine, which includes increased deposition of extracellular matrix material and growth inhibition of trabecular cells, a change in its concentration within the eye would have a profound effect because of this autoinductive activity. Transforming growth factor-beta 2 treatment of trabecular cells also increased their expression of the TGF-beta 1 gene. The authors previously showed that the level of TGF-beta 2 in the aqueous humor of glaucomatous eyes is significantly higher than that of age-matched nonglaucomatous controls. The current finding suggests that this growth modulator may exert its effects directly on the trabecular cells or that it may act indirectly through upregulating the production of TGF-beta 1.