Trabecular cell matrix metalloproteinase expression is transduced by protein kinase C

Purpose. Trabecular matrix metalloproteinases (MMPs) have been implicated in the regulation of aqueous humor outflow. Various growth factors, cytokines and cellular regulators modulate trabecular MMP expression, but little is known about the trabecular signal transduction pathways utilized. Methods. We utilized various protein kinase A and C (PKA and PKC) signal transduction pathway modulators and inhibitors to manipulate porcine trabecular cell production of MMPs and their tissue inhibitors, TIMPs. Western immunoblots and zymograms were utilized to evaluate trabecular production of these enzymes and their inhibitors in cell culture. Western immunoblots were also used to determine which PKA and PKC isozymes are present in trabecular cells. Results. PKA stimulators or inhibitors had minimal effects on trabecular MMP and TIMP production. PKC stimulators increased gelatinase B, stromelysin, collagenase and TIMP1 expression without dramatically affecting gelatinase A or TIMP2 levels. Inhibitors of PKC either reduced or blocked stimulation of these MMP and TIMP levels. The RII subunit of PKA is expressed by trabecular cells as are the α, βII, ε, ζ, ι, μ and possibly the λ isoforms of PKC. The δ, βI and γ isoforms of PKC are absent or are expressed at very low levels in trabecular cells. Conclusion. Trabecular cells utilize PKC as one major signal transduction pathway in modulating MMP and TIMP production. A discrete and limited profile of these protein kinase isoforms is expressed by trabecular cells.