Synthesis of extracellular matrix components by human ciliary muscle cells in culture

Different collagen types define two types of idiopathic epiretinal membranes

AIMS

To identify differences in extracellular matrix contents between idiopathic epiretinal membranes (IEM) of cellophane macular reflex (CMRM) or preretinal macular fibrosis (PMFM) type.

METHODS AND RESULTS

Idiopathic epiretinal membranes were analysed by light and quantitative transmission electron microscopy, immunohistochemistry and Western blotting. Substantial differences between CMRM and PMFM were observed regarding the nature of extracellular fibrils. In CMRM the fibrils were thin, with diameters between 6 and 15 nm. Between the fibrils, aggregates of long-spacing collagen were observed. In PMFM the diameters of fibrils measured either 18-26 or 36-56 nm. Using immunogold electron microscopy, 6-15 nm fibrils in CMRM were labelled for collagen type VI, while the fibrils in PMFM remained unstained. Using Western blotting and immunohistochemistry, a strong signal for collagen type VI was observed in all CMRM, while immunoreactivity was weak or absent in PMFM. In contrast, PMFM showed immunoreactivity for collagen types I and II, which was weak or absent in CMRM. Both types of membranes showed immunoreactivity for collagen types III and IV, laminin and fibronectin with similar intensity.

CONCLUSION

The presence of high amounts of collagen type VI in CMRM and the relative absence of collagen types I and II is the major structural difference to PMFM.

The mechanism of action of prostaglandins on uveoscleral outflow

It is generally accepted that prostaglandins (PGs) lower intraocular pressure by increasing uveoscleral outflow. The growing use of PGs to lower intraocular pressure has led to increased interest in the uveoscleral outflow. Uveoscleral outflow passes through extracellular spaces within the ciliary muscle and then through the suprachoroidal space to the posterior pole of the eye. Recent studies indicate that this reflects a direct effect of PGs on specific ciliary muscle prostanoid receptors. Activation of these receptors stimulates several linked responses, including cAMP formation and induction of c-Fos and c-Jun expression. These signals lead to increased biosynthesis of matrix metalloproteinases, a family of neutral proteinases that can cleave extracellular matrix molecules. These matrix metalloproteinases may initiate the alteration of collagens in the ciliary muscle to increase spaces among ciliary muscle fibers, thereby reducing hydraulic resistance in the uveoscleral outflow pathway.

Effect of latanoprost on the extracellular matrix of the ciliary muscle. A study on cultured cells and tissue sections

Prostaglandin F2alpha and its analogue latanoprost, both prostanoid FP receptor agonists, reduce the intraocular pressure mainly by enhancing uveoscleral outflow. Changes in the extracellular matrix of the ciliary muscle may be involved in the increased outflow. The effect of latanoprost and prostaglandin F2alpha on the extracellular matrix of the ciliary muscle was investigated. Cell cultures of human ciliary muscle were treated with latanoprost acid or prostaglandin F2alpha for 1-2 days and were immunostained against various extracellular matrix components and metalloproteinases. Proteinases were also analysed by zymography and by measuring plasmin generating ability. For comparison, matrix components were immunolocalized on tissue sections from monkey eyes, treated topically once daily with latanoprost for 10 days. In response to both prostaglandins collagens I, III, and IV, fibronectin, laminin and hyaluronan were reduced, while metalloproteinase -2 and -3 were increased. Zymography demonstrated the presence of functionally active metalloproteinase -2. Both prostaglandins enhanced the generation of plasmin, an activator of metalloproteinases. In the anterior part of the ciliary muscle in latanoprost-treated eyes immunostained collagen VI was decreased in 5 out of 5 monkeys and collagen IV was decreased in 4 of the 5 monkeys. These results suggest a role for latanoprost in the remodeling of extracellular matrix in the ciliary muscle. A latanoprost-induced change in the extracellular matrix might augment the flow of aqueous humour through the ciliary muscle bundles of the uveoscleral pathway.

Prostaglandin action on ciliary smooth muscle extracellular matrix metabolism: implications for uveoscleral outflow

The cellular mechanisms mediating intraocular pressure reduction following topical prostaglandin (PG) treatments are poorly understood. To determine if PG treatments might induce altered metabolism of extracellular matrix surrounding ciliary muscle cells, confluent human ciliary smooth muscle cell cultures were exposed to PGF 2 alpha' 17-phenyltrinor-PGF2 alpha' or 11-deoxy-PGE1 for one to four days and the distributions of collagen types I, III and IV as well as laminin were determined immunocytochemically. In addition, collagen type IV and promatrix metalloproteinase III (proMMP-3) content within treated cultures was determined using sandwich ELISAs. Compared with vehicle-treated cultures, there were substantial reductions in the density and branching of the collagen type IV-immunoreactive lattice accompanied by thickening of remaining strands in all PG-treated cultures. Similar changes were seen in the distribution of laminin within all PG-treated cultures. Reductions in collagen type III immunoreactivity were seen in cultures treated with either PGF2 alpha or 17-phenyltrinor-PGF2 alpha. No changes were observed in collagen type I immunoreactivity. Quantitative analyses revealed increased amounts of collagen type IV in both the culture medium and in extracts of the cell layer in all PG-treated cultures. In addition, there were substantial increases in the concentrations of proMMP-3 in all PG-treated cultures. These results indicate that PGs induce increased turnover and remodeling of ECM adjacent to ciliary muscle cells. Such changes may contribute to increased uveoscleral outflow in vivo following topical PG treatment.