Faculty Bibliography

PURPOSE: Intraocular pressure (IOP) regulation is largely unknown. SPARC-null mice demonstrate a lower IOP resulting from increased outflow. SPARC is a matricellular protein often associated with fibrosis. We hypothesized that SPARC overexpression would alter IOP by affecting extracellular matrix (ECM) synthesis and/or turnover in the trabecular meshwork (TM). METHODS: An adenoviral vector containing human SPARC was used to increase SPARC expression in human TM endothelial cells and perfused human anterior segments using multiplicities of infection (MOIs) 25 or 50. Total RNA from TM was used for quantitative PCR, while protein from cell lysates and conditioned media were used for immunoblot analyses and zymography. After completion of perfusion, the anterior segments were fixed, sectioned, and examined by light and confocal microscopy. RESULTS: SPARC overexpression increased the IOP of perfused human anterior segments. Fibronectin and collagens IV and I protein levels were elevated in both TM cell cultures and within the juxtacanalicular (JCT) region of perfused anterior segments. Collagen VI and laminin protein levels were increased in TM cell cultures but not in perfused anterior segments. The protein levels of pro-MMP-9 decreased while the kinetic inhibitors of metalloproteinases, TIMP-1 and PAI-1 protein levels, increased at MOI 25. At MOI 50, the protein levels of pro-MMP-1, -3, and -9 also decreased while PAI-1 and TIMP-1 and -3 increased. Only MMP-9 activity was decreased on zymography. mRNA levels of the collagens, fibronectin, and laminin were not affected by SPARC overexpression. CONCLUSIONS: SPARC overexpression increases IOP in perfused cadaveric human anterior segments resulting from a qualitative change the JCT ECM. Selective decrease of MMP-9 activity is likely part of the mechanism. SPARC is a regulatory node for IOP.

PURPOSE: Matrix metalloproteinase (MMP)-mediated turnover of extracellular matrix (ECM) affects outflow resistance in the uveoscleral pathway. The balance of MMPs and tissue inhibitors of metalloproteinases (TIMPs) governs the rate of ECM turnover in many tissues. The hypothesis was that a differential effect on MMPs and TIMPs in ciliary body smooth muscle (CBSM) cells would relate to the relative intraocular pressure-lowering effectiveness of the prostaglandin analogues (PGAs) bimatoprost, latanoprost, and unoprostone. METHODS: Human CBSM cells isolated from donor corneoscleral rims were incubated for 24 hours with control (0.015% ethanol in DMEM) or the free acid forms of bimatoprost (0.01 or 0.1 microg/mL), latanoprost (0.03 or 0.3 microg/mL), or unoprostone (0.145 or 1.45 microg/mL). Western blot analysis determined the relative protein concentrations of MMP-1, -2, -3. -9, and -24 as well as TIMP-1 through -4. Zymography measured the relative activity levels of MMP-1, -2, -3, and -9. RESULTS: All PGAs increased MMP-1, -3, and -9. Bimatoprost and latanoprost did not change MMP-2. Unoprostone decreased MMP-2 (21% +/- 3%). On zymography, MMP-1 and -2 did not change. Bimatoprost and latanoprost increased MMP-9 activity by 75% +/- 27% and 75% +/- 24%, respectively. MMP-3 activity was not detected on zymography. All PGAs increased TIMP-3, but only unoprostone increased TIMPs1 and -4 by 100% +/- 20% and 61% +/- 11%, respectively. TIMP-2 was unchanged by bimatoprost and latanoprost, but decreased by unoprostone (35% +/- 8%). CONCLUSIONS: Decreased MMP-2 with concurrent increases of TIMP-1 and -4 by unoprostone may explain the lower clinical efficacy of unoprostone. The MMP/TIMP balance relates to the observed intraocular pressure-lowering effectiveness in clinical studies with PGAs.

PURPOSE: To ascertain the expression pattern of alpha(2)-adrenergic receptors in the ciliary body (CB) and determine the effect of brimonidine on matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in ciliary body smooth muscle (CBSM) cells. METHODS: Qualitative RT-PCR was performed to detect the mRNA of the alpha(2)-adrenergic receptor subtypes alpha(2)A, alpha(2)B, and alpha(2)C in CB and CBSM cultures. Immunohistochemistry and immunoblot analysis were performed to further investigate alpha(2)A receptor expression in CB tissue and CBSM cells. CBSM cells from 15 different human donors received control or brimonidine tartrate (45 nM) for 1, 3, or 7 days. Changes in pro-MMP-1, -2, -3, -9, and -24 and TIMP-1, -2, -3, and -4 levels were evaluated by Western blot, with GAPDH as the endogenous control. Zymography was used to assess the activity of MMP-1, -2, -3, and -9. RESULTS: The mRNA of alpha(2)A, alpha(2)B, and alpha(2)C were detected in CB tissue and CBSM cells. Immunohistochemistry localized alpha(2)A receptors within the CB stroma. Immunoblot analysis demonstrated production by CBSM cells. Brimonidine increased pro-MMP-9 an average of 116% +/- 34% (P = 0.0360); enzymatic activity of MMP-9 was unchanged. TIMP-4 decreased an average of 25% +/- 8% (P = 0.0329) in conditioned medium, but increased 70% +/- 13% (P = 0.0057) in cell lysates. CONCLUSIONS: The presence of alpha(2)A, alpha(2)B, and alpha(2)C in CB tissue and CBSM cells indicates the possibility that brimonidine affects uveoscleral outflow. However, the changes in MMP-9 and TIMP-4 without significant changes in MMP-9 activity suggest that a role of the MMP/TIMP system in outflow is unlikely.