PURPOSE: Increased expression of stromelysin-1 (matrix metalloproteinase 
[MMP]-3) by the trabecular meshwork (TM) initiates extracellular matrix turnover 
and increases aqueous humor outflow facility. Tumor necrosis factor (TNF)alpha 
and interleukin (IL)-1alpha are efficacious inducers of MMP-3 in TM. To 
facilitate understanding of the regulation of MMP-3, the authors investigated 
the involvement of p38 MAP kinase pathway proteins in this process.
METHODS: Western immunoblots were used to determine the effects of these 
cytokines and p38 MAP kinase pathway inhibitors on MMP-3 protein levels, p38 MAP 
kinase isoforms, and phosphorylation levels in human and porcine TM cells. The 
effects of a dominant-negative p38 MAP kinase construct on MMP-3 expression were 
evaluated. Morphologic changes in the cells were also examined.
RESULTS: Both cytokines increased MMP-3 levels. The p38 MAP kinase inhibitor 
SB202190 diminished MMP-3 induction by TNFalpha at all times and at 24 hours by 
IL-1alpha but potentiated the IL-1alpha-induced increase in MMP-3 at later 
times. MMP-3 induction by both cytokines was blocked by dominant-negative p38 
MAP kinase constructs. Each cytokine increased phosphorylation of the p38 MAP 
kinase pathway components and altered TM cell morphology. The p38 inhibitor 
blocked only the morphologic changes produced by TNFalpha. Human and porcine TM 
cells expressed p38 alpha, beta, delta, and gamma isoforms, which migrate 
coincident with bands of specific phosphorylation.
CONCLUSIONS: The effects of p38 inhibitors and the dominant-negative construct 
on TNFalpha and IL-1alpha induction of MMP-3 demonstrate an essential role for 
p38 in this signaling process. Differences between p38 inhibitor effects on 
TNFalpha and IL-1alpha induction of MMP-3 suggest divergent p38 isoform use, as 
do the morphologic responses. The anomalous p38 inhibitor effect on IL-1alpha 
induction of MMP-3 and phosphorylation of p38 delta/gamma suggests complex 
interactions between p38 MAP kinase isoforms and their differential uses by 
TNFalpha and IL-1alpha in TM.