Transretinal degeneration in ageing human retina: a multiphoton microscopy analysis

AIM

Retinal cell remodelling has been reported as a consistent feature of ageing. However, the degree to which this results in transretinal degeneration is unclear. To address this, the authors used multiphoton microscopy to quantify retinal degeneration in post-mortem human eyes of two age groups.

METHODS

Retinas from six young subjects (18-33 years old) and six older subjects (74-90 years old) were prepared as wholemount preparations. All retinas were stained with 4,6-diamidino-2-phenylindole and imaged by multiphoton confocal microscopy to quantify neuron densities in the retinal ganglion cell layer (RGCL), inner nuclear layer (INL) and outer nuclear layer (ONL). Neurons were counted using automated cell identification algorithms. All retinas were imaged hydrated to minimise tissue artefacts.

RESULTS

In both groups, 56% of the area within the central 4 mm eccentricity and 27% of the area with eccentricity between 4 mm and 7 mm were imaged. Compared with young subjects, the peak RGCL neuron loss in the aged subjects (25.5%) was at 1 mm eccentricity. INL and ONL neuron densities significantly decreased at 1-2 mm eccentricity (8.7%) and 0.5-4 mm eccentricity (15.6%) respectively (P <0.05). The reduction in neuron density in the INL corresponded, spatially, to the region with the greatest neuron loss in the RGCL and ONL.

CONCLUSIONS

This is the first study to correlate neurodegeneration in different populations of cells in the ageing retinas. These data confirm that the greatest neuronal loss occurs in the RGCL and ONL in human ageing retinas, whereas the INL is relatively preserved.

Topography of neuron loss in the retinal ganglion cell layer in human glaucoma

AIM

To determine if retinal ganglion cell (RGC) loss influences the loss of surrounding RGCs to generate clustered patterns of cell death in human glaucoma. It is hypothesised that retinal ganglion cell loss accelerates the loss of surrounding cells to generate, at a local, cellular scale, clustered patterns of retinal of RGC death. The absence of these interactions would result in a diffuse pattern RGC loss.

METHOD

Six glaucomatous retinas (67-83 years old) and six age-matched control retinas (61-89 years old) were prepared as wholemounts and stained by 4',6-diamidino-2-phenylindole (DAPI) solution (3 microg/ml in PBS). An area corresponding to central 14 degrees of the visual field was imaged. The nearest-neighbour distribution was determined for cells in both normal and glaucomatous RGCL.

RESULTS

Clustered RGC loss in human glaucoma was observed on a background of diffuse loss. The mean nearest-neighbour distance (NND) of the glaucomatous retinas was significantly higher than with controls (p<0.001). The distribution of NND in glaucomatous retinas was skewed to the higher values with a higher positive kurtosis relative to controls. The quantitative analysis of the pattern of cell loss is supported by the visual inspection of the patterns of cell loss.

DISCUSSION

The nearest-neighbour analysis is consistent with the presence of two patterns of cell loss in the RGCL in glaucoma. While the diffuse of cell loss can account for an overall reduction in the RGC population, an additional non-random pattern is consistent with the hypothesis that RGC loss has a local influence on the viability of surrounding cells.

Platelets interact with tissue factor immobilized on surfaces: effects of shear rate

BACKGROUND

While procoagulant activities of Tissue Factor (TF) have been widely investigated, its possible pro-adhesive properties towards platelets have not been studied in detail.

MATERIAL AND METHODS

We explored the interaction of platelets with human Tissue Factor (hTF) firmly adsorbed on a synthetic surface of polyvinilidene difluoride (PVDF) using different shear rates. For studies at 250 and 600 s(-1), TF firmly adsorbed was exposed to flowing anticoagulated blood in flat perfusion devices. Deposition of platelets and fibrin were evaluated by morphometric, immunocytochemical and ultrastructural methods. Prothrombin fragment 1 + 2 (F1 + 2) levels were also measured. Experiments at 5000 s(-1), were performed on the Platelet Function Analyzer (PFA-100) with experimental cartridges with collagen (COL) or collagen-hTF (COL + TF). Haemostatic effect of recombinant activated FVIIa (rFVIIa) was assessed in the same experimental settings.

RESULTS

Platelet deposition on hTF reached 19.8 +/- 1.3% and 26.1 +/- 3.4% of the total surface, at 250 and 600 s(-1), respectively. Fibrin formation was significantly higher at 250 s(-1) than at 600 s(-1) (P < 0.05). The addition of rFVIIa did not influence platelet deposition but raised fibrin formation and thrombin generation at both shear rates (P < 0.05). At 5000 s(-1), closure times (CT) in the PFA-100 were significantly shortened in the presence of hTF (154.09 +/- 14.69 s vs. 191.45 +/- 16.09 s COL alone; P < 0.05). Addition of rFVIIa did not cause a further reduction of CT.

CONCLUSIONS

Our studies demonstrate that hTF is an adhesive substrate for platelets and suggest that the von Willebrand factor could mediate these interactions. At low and intermediate shear rates, rFVIIa enhanced the procoagulant action of hTF, but this effect was not observed at very high shear rates.

4-Hydroxynonenal, a product of oxidative stress, leads to an antioxidant response in optic nerve head astrocytes

Oxidative stress has been implicated in the pathogenesis of several neurodegenerative disorders including primary open-angle glaucoma (POAG) an optic neuropathy characterized by loss of retinal ganglion cell (RGC) axons and remodeling of the optic nerve head (ONH). Previous findings in glaucomatous astrocytes suggested increased oxidative stress and lipid peroxidation in human optic nerves. We studied the dose and time dependent effects of 4-hydroxynonenal (HNE), a by-product of lipid peroxidation, on the viability of primary cultures of human ONH astrocyte. A significant depletion of glutathione (GSH) level was observed in normal astrocytes after exposure to HNE for 1 h and 3 h. Untreated glaucomatous astrocytes exhibited depleted levels of GSH which increased slightly after exposure to HNE. Both normal and glaucomatous astrocytes recovered GSH levels after 24 h of removal of HNE. HNE caused significant increases in expression of antioxidant enzymes, glutamate cysteine ligase catalytic subunit (GCLC), aldo-keto reductase 1C family member 1 (AKR1C1) and glutathione S-transferase-alpha4 (GSTA4). HNE induced expression of the transcription factor Nrf2, which coordinates the upregulation of detoxification enzymes. In addition, ONH astrocytes responded to HNE by activation and transcription of cFOS and NFkB, which regulate physiological protective responses against oxidative stress. Our results indicate that ONH astrocytes exhibit a strong antioxidant response to HNE treatment by inducing the transcription factors cFOS, NFkB, and Nrf2, which upregulate the expression of GCLC, to produce more GSH in the cell. AKR1C1 was also upregulated after HNE treatment to inactivate HNE, independent of GSH availability in the cells. Collectively these data indicate that ONH astrocytes can efficiently counteract the neurotoxic effects of HNE offering protection in the optic nerve by releasing GSH and antioxidant enzymes to eliminate the products of chronic oxidative stress.

Long-term activation of c-Fos and c-Jun in optic nerve head astrocytes in experimental ocular hypertension in monkeys and after exposure to elevated pressure in vitro

This study investigates whether the immediate early gene (IEG) products c-Fos and c-Jun are activated in vivo in monkeys with experimental glaucoma, and in vitro in cultured human ONH astrocytes exposed to hydrostatic pressure (HP). Three Rhesus monkeys with mild glaucomatous damage (mean intraocular pressure (IOP) 27 +/- 1.3 mm Hg approximately 42 weeks) and three with moderate glaucomatous damage (mean IOP 44 +/- 6.7% mm Hg approximately 11 weeks) were used for this study; the contralateral eye served as normal control (mean IOP 18.6 +/- 1.7 mm Hg). ONH tissues were stained with GFAP, DAPI, and c-Jun or c-Fos, and transcription factor positive and negative nuclei were counted to determine nuclear localization. Cultured human normal and glaucomatous ONH astrocytes exposed to elevated HP served as the in vitro model of elevated pressure. Activation and nuclear localization of c-Fos and c-Jun increased significantly in the monkeys with elevated IOP. These data correlated with axonal loss, reactive astrocytes, and remodeling of the optic disc. Cultured human ONH astrocytes showed increased nuclear localization of c-Fos and c-Jun under exposure to HP. Immunohistochemistry demonstrated that the upstream regulators of c-Fos and c-Jun, ERK-MAPK and MAPKp38 localized to the nuclei of ONH astrocytes in monkeys with experimental glaucoma. Taken together, these results demonstrate c-Fos and c-Jun activation in ONH astrocytes in vivo and in vitro, and that activation of both transcription factors is associated with ERK and MAPKp38 activation in experimental glaucoma, suggesting that activation of transcription factors may participate in the induction and maintenance of the reactive astrocyte phenotype in glaucomatous optic neuropathy.

Antithrombotic effect of a new nitric oxide donor (LA419) on experimental thrombogenesis

BACKGROUND

The ability of nitrous compounds to donate nitric oxide (NO), an agent with vasodilating and inhibitory effects on platelet function, has been considered a useful pharmacologic strategy for cardiovascular complications. The purpose of this study was to investigate the effects of a new NO donor, LA419, on platelet interaction in an ex vivo model with human blood circulating through collagen-rich surfaces.

MATERIALS AND METHODS

Platelet adhesive and cohesive function were analyzed by morphometric procedures after perfusion techniques. Treated blood was exposed to thrombogenic surfaces and platelet interactions were morphometrically evaluated.

RESULTS

All the concentrations studied of LA419 (10 microM, 20 microM and 100 microM) reduced overall platelet interaction with a collagen surface (27.19 +/- 4.72; 25.52 +/- 3.52; and 23.44 +/- 3.01, P < 0.05, respectively, vs. 32.31 +/- 1.61% in the control). The antithrombotic effect was confirmed by results in cross-sectional studies performed in arterial vessels exposed to circulating blood. Values of thrombus and covered surface at 20 microM LA419 were, respectively, 13.67 +/- 4.97% and 19.01 +/- 5.89%; respect to controls 34.80 +/- 5.29% and 37.93 +/- 5.34% (P < 0.05). Moreover, LA419 reduced significantly thrombus area (88.45 +/- 21.97 microm(2); P < 0.05) with respect to controls (168.45 +/- 21.97 microm(2)) and thrombus height, from an average of 10.27 +/- 1.05 microm in nontreated blood to 7.16 +/- 0.6 microm in treated samples (P < 0.05).

CONCLUSION

From the present data we can conclude that LA419 possesses a strong antiplatelet action, as demonstrated by its ability to significantly inhibit the interaction of platelet with highly thrombogenic collagen surfaces.

Evaluation of effects of rofecoxib on platelet function in an in vitro model of thrombosis with circulating human blood

BACKGROUND

Cyclooxygenase (COX)-2-selective non-steroidal anti-inflammatory drugs have been used for anti-inflammatory therapy. However, it has also been described that they may increase risk of cardiovascular events.

OBJECTIVES

To study the effects of COX2 inhibitor rofecoxib on platelet function using in vitro tests. Results were compared with those obtained in a parallel experiment with acetyl salicylic acid (ASA).

METHODS

Studies of platelet aggregation, using different agonists, were performed by a turbidimetric method. Adhesive and cohesive function of platelets were analyzed by perfusion techniques, treated blood was exposed to thrombogenic surfaces and platelet interaction was morphometrically evaluated.

RESULTS

Twenty-five micro M of rofecoxib induced a prolonged lag time and a reduction in the percentage of aggregation when arachidonic acid, ADP or collagen were used as agonists. In perfusion studies with parallel chamber rofecoxib 50 microM and ASA 500 microM reduced overall platelet interaction with the collagen surface (17.4 +/- 3.7, P < 0.05; vs. 32.1 +/- 2.6%P < 0.05 and 17.9 +/- 2.4, vs. 31.9 +/- 3.24, P < 0.05, respectively). In studies performed on annular chambers, 25 micro M of rofecoxib reduced platelet interaction; values of the thrombus and covered surface were 17.4 +/- 4.5%; P < 0.05 and 21.1 +/- 4.1%; P < 0.05, respectively, vs. 30.4 +/- 7.5% and 33.5 +/- 6.5 in the control. ASA did also impair thrombus formation but differences did not reach the levels of statistical significance. Moreover, rofecoxib but not ASA reduced significantly thrombus height and thrombus area (7.4 +/- 0.5 microM; P < 0.005 and 96.0 +/- 21.2 microM(2); P < 0.05 vs. control 11.2 +/- 0.9 microM and 220.0 +/- 47.7 microM(2), respectively).

CONCLUSION

We conclude that under our experimental conditions, rofecoxib diminished platelet aggregation induced by different agonists and inhibited platelet-mediated thrombogenesis in an in vitro model of thrombosis.

Altered expression of 3 alpha-hydroxysteroid dehydrogenases in human glaucomatous optic nerve head astrocytes

3alpha-hydroxysteroid dehydrogenase (3alpha-HSD) isoforms (AKR1C1-AKR1C4) are aldo-keto reductases that metabolize steroids and other substances in many tissues including the CNS. Here we demonstrated that in glaucomatous human optic nerve heads, increased expression of 3alpha-HSD was localized to reactive astrocytes in the lamina cribrosa. Similar, optic nerve head astrocytes exhibited increased expression of 3alpha-HSD in response to elevated intraocular pressure in a monkey model of experimental glaucoma, but not in monkeys with unilateral optic nerve transection. In vitro, glaucomatous optic nerve head astrocytes expressed higher levels of AKR1C1, AKR1C2, and AKR1C3 mRNA, than normal astrocytes, with significant differential increase of AKR1C2 expression, and exhibited higher enzymatic activity forming 3alpha-androstanediol a well-recognized neurosteroid. Normal astrocytes exposed to elevated hydrostatic pressure selectively increased AKR1C2 expression. Our findings of increased expression of 3alpha-HSDs in glaucomatous optic nerve head astrocytes offer new insights into possible roles for neurosteroids in the pathophysiology of glaucoma.

Differential expression of matrix metalloproteinases in monkey eyes with experimental glaucoma or optic nerve transection

Extracellular matrix (ECM) remodeling after neuronal injury and reactive gliosis is carried out by activation of matrix metalloproteinases (MMPs) regulated by their tissue inhibitors (TIMPs). In glaucoma, there is a loss of retinal ganglion cells and extensive ECM remodeling (cupping) at the level of the optic nerve head, frequently associated with elevated intraocular pressure. To determine whether ECM remodeling in the glaucomatous optic nerve head occurs in response to loss of axons or to elevated intraocular pressure we compared the patterns of MMP and TIMP expression in the eyes of monkeys with laser-induced glaucoma or with optic nerve transection. MT1-MMP and MMP1 expression was markedly increased in reactive astrocytes in optic nerve heads with experimental glaucoma but not in the optic nerve head of transected eyes. In normal control eyes retinal ganglion cells expressed MMP2, TIMP1 and TIMP2 constitutively, and the proteins were detected in their axons. At the site of transection, MT1-MMP, MMP1, MMP2, TIMP1 and TIMP2 were expressed by reactive astrocytes. Inflammatory cells, fibroblasts and reactive astrocytes at the transected site expressed MMP3 and MMP9, which were undetectable in the retina and optic nerve head in any condition. Constitutive expression of MMP2, TIMP1 and TIMP2 in retinal ganglion cells suggests a role in maintenance of synaptic integrity and plasticity and maintenance of the periaxonal space. Increased MMP1 and MT1-MMP1 expression in the glaucomatous optic nerve head is specific to tissue remodeling due to elevated intraocular pressure and not secondary to loss of axons.

Expression of small heat shock proteins and intermediate filaments in the human optic nerve head astrocytes exposed to elevated hydrostatic pressure in vitro

The small heat shock proteins (sHSP), alpha B-crystallin and Hsp27 are chaperone molecules that maintain the integrity of intermediate filament (IF) network and prevent unfolding of cellular proteins induced by stress. In the optic nerve head (ONH) of eyes with glaucoma, reactive astrocytes expressed Hsp27, perhaps in response to stress related to elevated intraocular pressure. In this study, we determined the effect of elevated hydrostatic pressure (HP) in the synthesis, distribution and co-localization of alpha B-crystallin and Hsp27 with IF in cultured ONH astrocytes. Astrocyte monolayers were pressurized to 60 mm Hg (92% air 8% CO(2)) and incubated at 37 degrees C for 6, 24 or 48 hr. Controls were exposed to ambient pressure. Cells were analyzed by immunocytochemistry, Western blot and immunoprecipitation using antibodies to Hsp27, alpha B-crystallin, vimentin or GFAP. Control astrocytes seemed flat, polygonal with short processes. alpha B-crystallin appeared granular in the perinuclear area and filamentous in the cell periphery. Fine granular Hsp27 was distributed throughout the cytoplasm. GFAP and vimentin co-localized with Hsp27 in the cytoplasm. Astrocytes exposed to HP were star-shaped with long processes. Hsp27 was condensed in large granules around the nucleus. GFAP and vimentin co-localized with Hsp27 and alpha B-crystallin in the perinuclear area. Western blot and metabolic labeling detected increased synthesis of Hsp27, GFAP and vimentin but no change in alpha B-crystallin. These results indicated that GFAP and vimentin associate with Hsp27 and alpha B-crystallin in ONH astrocytes. HP affected the integrity of the cytoskeleton consistent with morphological changes. Small HSP may reinforce and maintain IF integrity in response to HP.

Expression of myocilin/TIGR in normal and glaucomatous primate optic nerves

Myocilin/TIGR was the first molecule discovered to be linked with primary open angle glaucoma (POAG), a blinding disease characterized by progressive loss of retinal ganglion cells. Mutations in myocilin/TIGR have been associated with age of disease onset and severity. The function of myocilin/TIGR and its role in glaucoma is unknown. Myocilin/TIGR has been studied in the trabecular meshwork to determine a role in regulation of intraocular pressure. The site of damage to the axons of the retinal ganglion cells is the optic nerve head (ONH). The myocilin/TIGR expression was examined in fetal through adult human optic nerve as well as in POAG. Myocilin/TIGR was expressed in the myelinated optic nerve of children and normal adults but not in the fetal optic nerve before myelination. Also examined was the expression in monkeys with experimental glaucoma. The results demonstrate that optic nerve head astrocytes constitutively express myocilin/TIGR in vivo in primates. Nevertheless, myocilin/TIGR is apparently reduced in glaucomatous ONH. The colocalization of myocilin/TIGR to the myelin suggests a role of myocilin/TIGR in the myelinated optic nerve.

Increased elastin expression in astrocytes of the lamina cribrosa in response to elevated intraocular pressure

PURPOSE

To determine whether abnormal elastin synthesis in the glaucomatous optic nerve head and lamina cribrosa is due to elevated intraocular pressure (IOP) or secondary to axonal injury, monkeys with elevated IOP and with optic nerve transection were compared.

METHODS

Unilateral, chronic elevated IOP was induced in 11 rhesus monkeys by laser scarification of the trabecular meshwork. IOP was monitored weekly and maintained within 25 to 45 mm Hg for 7 to 36 weeks. In 6 monkeys, unilateral, optic nerve transection was performed, and monkeys were killed after 4 weeks. Optic nerve damage was assessed by stereoscopic slit-lamp biomicroscopy and fundus photography and by confocal scanning laser ophthalmoscopy. The eyes were enucleated and processed for immunohistochemistry and in situ hybridization and for electron microscopic immunogold detection of elastin. Axonal loss was evaluated in cross sections of the optic nerve stained with phenylenediamine.

RESULTS

Compared with normal contralateral controls, the lamina cribrosa of eyes with elevated IOP exhibited markedly increased elastin and the presence of elastotic aggregates in the extracellular matrix and upregulation of elastin mRNA in the astrocytes. In transected eyes, elastin appeared as fine fibers in the lamina cribrosa, without elastotic aggregates, and without new synthesis or abnormal deposition of elastin. At the transected site, new synthesis of elastin was present in the pia mater but not in astrocytes in the glial scar.

CONCLUSIONS

This study demonstrates that abnormal elastin synthesis in experimental glaucomatous optic neuropathy in the monkey is specific to elevated IOP and not secondary to axonal loss. The mechanisms by which elevated IOP induces enhanced elastin synthesis in laminar astrocytes are unknown but differ from those involved in acute axonal injury such as transection, where inflammation and breakdown of the blood-nerve barrier occur.

Effect of anticoagulants on activation of polymorphonuclear leukocytes induced by shear stress

We analyzed how actin polymerization, CD11b expression and homotypic aggregation could be used as markers to study leukocyte activation. Leukocytes were obtained from blood anticoagulated with: citrate, unfractioned heparin (UH) and low molecular weight heparin (LMWH). Flow cytometry was used to study actin polymerization and expression of CD11b after leukocyte exposure to shear stress. Leukocyte aggregation was microscopically assessed. Shear increased both actin polymerization and expression of CD11b in citrated blood (100.1&#x00B1;7.1 vs. 85.8&#x00B1;8.5 p&#x003C; 0.05 and 53.5&#x00B1;3.5 vs. 20.7&#x00B1;5.1; p&#x003C; 0.005 respectively). These parameters remained unmodified in UH samples. Using both anticoagulants together, we observed increase in CD11b expression induced by shear stress (59.3&#x00B1;2.1 vs. 25.1&#x00B1;11.0; p&#x003C; 0,05). LMWH samples showed higher basal levels of actin polymerization and CD11b expression than citrated samples (237&#x00B1;40.8, vs. 85.8&#x00B1;8.5 p&#x003C; 0.05 and 47.8&#x00B1;2.6, vs. 20.7&#x00B1;5.1; p&#x003C; 0.005) but no changes induced by shear were observed. When LMWH was used in combination with citrate we observed a decrease in basal activation and significant modifications in CD11b expression induced by shear stress (80.0&#x00B1;4.1 vs. 50.4&#x00B1;2.7). Leukocyte aggregation was modified by UH at basal levels and by LMWH after shear stress. These results indicate that exposure to shear stress results in leukocyte activation. The choice of anticoagulant is a crucial factor in studies of leukocyte function.

In vitro evaluation of reactive astrocyte migration, a component of tissue remodeling in glaucomatous optic nerve head

In order to improve understanding of remodeling events in the glaucomatous optic nerve head, the migration of optic nerve head astrocytes was studied in vitro. Since elevated intraocular pressure is an important stress factor identified in glaucomatous eyes, optic nerve head astrocytes were incubated under physical stress created by elevated hydrostatic pressure. In addition, they were incubated in the presence of a chemical stimulus, lipolysaccharide (LPS). Migration of reactivated astrocytes in the presence of these stressors was examined using chambers in which cell migration through extracellular matrix-coated pores is only possible following proteolytic digestion of the matrix. We observed that the migratory ability of optic nerve head astrocytes was approximately 4-6 times greater following exposure to elevated hydrostatic pressure or LPS for up to 48 h. Phosphoinositide 3-kinase, protein kinase C, and tyrosine kinase were found to be involved in the signal transduction for activated migration of optic nerve head astrocytes in response to elevated hydrostatic pressure or LPS. In addition, we observed that the stress-induced migration of optic nerve head astrocytes, which is accompanied by proteolytic degradation, resulted in the formation of culture cavities containing mucopolysaccharides. These in vitro findings provide a clearer understanding of the pathophysiologic mechanisms of characteristic tissue remodeling events that occur, in vivo, in the glaucomatous optic nerve head.

Expression of matrix metalloproteinases and tissue inhibitors of metalloproteinases in human optic nerve head astrocytes

Glaucomatous optic neuropathy is a common blinding disease characterized by remodeling of the extracellular matrix (ECM) and loss of retinal ganglion cell (RGC) axons at the level of the optic nerve head (ONH). Astrocytes, the major cell type in ONH, may participate in this process by production of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs). In normal and glaucomatous ONH, we detected MMP and TIMP expression by immunohistochemistry. Cultured astrocytes were used to characterize expression of MMPs and TIMPs by zymography, Western blot, and RNase protection assay. MMP production was stimulated with phorbol 12-myristate 13-acetate (PMA). Astrocytes expressed MMP1, MT1-MMP, MMP2, TIMP1, and TIMP2 in normal and glaucomatous ONH. MMP2, TIMP1, and TIMP2 localized to RGCs and their axons. Increased MMP1 and MT1-MMP expression was demonstrated in glaucoma. Cultured astrocytes constitutively expressed MMP2, MT1-MMP, TIMP1, and TIMP2, whereas MMP3, MMP7, MMP9, and MMP12 were not detectable in tissues or in cultured astrocytes. Our findings demonstrate the presence of specific MMPs and TIMPs in the ONH that may participate in the homeostasis and remodeling of the ECM in glaucoma. Expression of the same MMPs and TIMPs in cultured ONH astrocytes will allow further studies on the mechanisms regulating these enzymes.

Induction of HLA-DR expression in human lamina cribrosa astrocytes by cytokines and simulated ischemia

PURPOSE

Recent evidence strongly suggests that activated immunity occurs during the neurodegenerative process of glaucomatous optic neuropathy. Although activation of lamina cribrosa astrocytes has been identified in glaucomatous optic nerve head, their role on the activated immune responses seen in glaucoma patients is unknown. Here, the authors aimed to study the potential role of lamina cribrosa astrocytes as a component of activated immune responses seen in glaucoma patients.

METHODS

Expression of HLA-DR in optic nerve head astrocytes was studied using immunohistochemistry in postmortem eyes of patients with glaucoma and normal donors. Serum cytokine levels of patients with glaucoma and control subjects were measured using enzyme-linked, immunosorbent assay. In addition, in vitro experiments were performed using astrocyte cultures derived from human optic nerve head or fetal human brain. The cultured astrocytes were incubated under selected stress conditions such as exposure to cytokines, IFN-gamma and IL-10, or simulated ischemia for up to 48 hours. The expression of HLA-DR was studied in these cells using flow cytometry and immunocytochemistry.

RESULTS

Immunohistochemistry demonstrated an upregulation of the HLA-DR expression in the optic nerve head astrocytes in glaucoma. In addition, serum levels of IL-10 was higher in the patients with normal pressure glaucoma compared to age-matched control subjects (P: = 0.001). Regarding in vitro experiments, unlike brain astrocytes, the percentage of cells expressing HLA-DR was approximately 3 times higher in the cultures of optic nerve head astrocytes exposed to simulated ischemia compared to cultures incubated under normal conditions (P: = 0.09). Incubation with IFN-gamma induced HLA-DR expression in brain and lamina cribrosa astrocytes, up to 25-fold, (P < 0.001) either in the absence or presence of simulated ischemia. Induction of HLA-DR expression by IL-10 was approximately 6 times higher in lamina cribrosa astrocytes incubated under simulated ischemia compared to that incubated under normal condition (P: = 0.004) and was not prominent in brain astrocytes.

CONCLUSIONS

These findings suggest that optic nerve head astrocytes function as antigen-presenting cells and that their immunogenic capacity is more sensitive to ischemia than brain astrocytes. Taken together, these findings provide novel evidence that regulation of immunogenic capacity of optic nerve head astrocytes by cytokines or ischemic stress may have a role during the neurodegeneration process in patients with glaucoma.

Hydrostatic pressure stimulates synthesis of elastin in cultured optic nerve head astrocytes

Elastin is a major component of the extracellular matrix (ECM) of the lamina cribrosa in the optic nerve head in humans and nonhuman primates. The lamina cribrosa appears to be the site of damage to the retinal ganglion cell axons in glaucomatous optic neuropathy, characterized in many patients by elevated intraocular pressure (IOP). Type 1B astrocytes are the major cell type in the lamina, synthesize elastic fibers during development, express increased elastin mRNA, and synthesize abnormal elastin in glaucoma. In this study, we determined the effect of elevated hydrostatic pressure on the synthesis of elastin by type 1B astrocytes in culture. Type 1B astrocytes were exposed to gradients of hydrostatic pressure and tested for proliferation, morphology, synthesis, and deposition of elastin. Trichloroacetic acid (TCA) and immunoprecipitation of radiolabeled protein determined total new protein and elastin synthesis. Proteins from the conditioned media were analyzed by Western blot. Levels of elastin mRNA were determined by in situ hybridization. Cell proliferation increased approximately 2-fold after exposure to pressure for one day, approximately 5-fold after 3 and 5 days of exposure to pressure. Confocal and electron microscopic cytochemistry showed a marked increase in intracellular elastin in astrocytes exposed to pressure, as compared with controls. Intracellular elastin was associated with the RER-Golgi region and with the cytoskeleton. Total protein and elastin synthesis increased significantly (P < 0.05) at 3- and 5-day exposure to pressure, as well as the level of elastin mRNA. Elastin protein in the media increased with the level of pressure. These results indicate that hydrostatic pressure stimulates type 1B astrocytes to synthesize and secrete soluble elastin into the media. In glaucoma, type 1B astrocytes may respond to IOP-related stress with increased expression of elastin and formation of elastotic fibers leading to loss of elasticity and tissue remodeling.

Selective expression of neural cell adhesion molecule (NCAM)-180 in optic nerve head astrocytes exposed to elevated hydrostatic pressure in vitro

Glaucomatous optic neuropathy is usually associated with elevated intraocular pressure. Optic nerve head astrocytes may respond to intraocular pressure by stimulation of pressure-sensitive mechanoreceptors on the cell surface. Neural cell adhesion molecule (NCAM) a transmembrane protein, mediates cell adhesion and migration. The NCAM 180 isoform increases in astrocytes of glaucomatous optic nerve head. We characterized the relative expression of NCAM isoforms in human optic nerve head astrocytes grown under elevated hydrostatic pressure. Astrocytes cultured from normal human optic nerve heads were exposed to either atmospheric or continuous hydrostatic pressure of 60 mm Hg, and analyzed at 6-48 h. Changes in cell shape, immunoreactivity, and distribution of GFAP, actin and NCAM were observed in pressure-treated cultures. Newly synthesized (35)S-labeled NCAM protein immunoprecipitated from cell lysates was increased 2-fold within 24 h after exposure to elevated pressure compared to control. The increase in NCAM synthesis was primarily due to the NCAM 180 isoform. A significant increase in NCAM 180 mRNA levels was detected by RT-PCR and Northern blots in cultured optic nerve head astrocytes within 6 h after exposure to elevated pressure. NCAM 180 mRNA and protein synthesis decreased after 24 h and returned to control levels by 48 h. Our data indicate that NCAM 180 transcription and synthesis in astrocytes is stimulated by elevated hydrostatic pressure. Because NCAM 180 interacts with the cytoskeleton through an extended cytoplasmic tail, a selective and transient increase in NCAM 180 in optic nerve head astrocytes exposed to elevated pressure may be relevant to the migration and interactions of reactive astrocytes in glaucoma.

Synthesis of elastic microfibrillar components fibrillin-1 and fibrillin-2 by human optic nerve head astrocytes in situ and in vitro

The purpose of this study was to identify elastic microfibrillar components fibrillin-1 and fibrillin-2 in optic nerve heads of adult normal and glaucomatous subjects, in cultured optic nerve head astrocytes (type 1B astrocytes), as well as fibrillin-1 in fetal optic nerve heads. To characterize synthesis and gene expression of microfibrillar proteins in human optic nerve heads and cultured type 1B astrocytes, light microscopy immunohistochemistry, in situ hybridization, and RT-PCR or Northern blots were performed. Our results demonstrated that fibrillin-1 was associated with blood vessels, astrocytes in the glial columns and cribriform plates, and with astrocyte processes in the nerve bundles in all samples. In glaucomatous optic nerves there was enhanced fibrillin-1 immunoreactivity, especially surrounding blood vessels. Fibrillin-2 was localized primarily to blood vessels in all samples, without qualitative differences between normal and glaucomatous samples. In fetal optic nerve heads fibrillin-1 mRNA was localized to glial cells and to the blood vessel walls. In adult optic nerve heads, there was little fibrillin-1 mRNA as detectable by in situ hybridization and RT-PCR. There was no detectable upregulation of fibrillin-1 mRNA in glaucoma. In cultured type 1B astrocytes, fibrillin-1 staining was mostly pericellular. There was little fibrillin-2 immunoreactivity. In conclusion, astrocytes from the optic nerve head deposit elastic microfibrillar components in situ and in vitro, with a predominance of fibrillin-1. Upregulation of fibrillin-1 mRNA was not observed in glaucoma, suggesting that increased transcription may occur early in the disease process. Cultures of type 1B astrocytes from the optic nerve head provides a useful model to study mechanisms regulating the interactions of elastin and the microfibrils in optic nerve head astrocytes.

The optic nerve head in glaucoma: role of astrocytes in tissue remodeling

Primary open angle glaucoma is a common eye disease characterized by loss of the axons of the retinal ganglion cells leading to progressive loss of vision. The site of damage to the axons is at the level of the lamina cribrosa in the optic nerve head. The mechanism of axonal loss is unknown but elevated intraocular pressure and age are the most common factors associated with the disease. Previous studies in human glaucoma and in experimental glaucoma in monkeys have established a relationship between chronic elevation of intraocular pressure and remodeling of the optic nerve head tissues known clinically as cupping of the optic disc. This review focuses on the astrocytes, the major cell type in the optic nerve head. Astrocytes participate actively in the remodeling of neural tissues during development and in disease. In glaucomatous optic neuropathy, astrocytes play a major role in the remodeling of the extracellular matrix of the optic nerve head, synthesize growth factors and other cellular mediators that may affect directly, or indirectly, the axons of the retinal ganglion cells. Due to the architecture of the lamina cribrosa, formed by the cells and the fibroelastic extracellular matrix, astrocytes may respond to changes in intraocular pressure in glaucoma, leading to some of the detrimental events that underlie axonal loss and retinal ganglion cell degeneration.

Responses of different cell lines from ocular tissues to elevated hydrostatic pressure

BACKGROUND/AIMS

Mechanical forces are thought to induce cellular responses through activation of signalling pathways. Cells within the intraocular environment are exposed to constant changes in the levels of intraocular pressure. In this study, an attempt was made to determine the acute effects of elevated hydrostatic pressure on different intraocular cells grown in culture.

METHODS

Different cell lines derived from ocular tissues including non-pigmented and pigmented ciliary epithelium, trabecular meshwork, retina, and lamina cribrosa were incubated in a pressurised chamber at 50 mm Hg in a culture incubator at 37 degrees C for up to 6 hours. Control cells were incubated at atmospheric pressure. The viability of the cells was examined using their intracellular esterase activity. The morphology and cytoskeleton of the cells were investigated using microscopy and phalloidin staining. Adenylyl cyclase activity was assessed by measuring the conversion of [(3)H]-cAMP from [(3)H]-ATP in response to elevated hydrostatic pressure for 1-6 hours. In addition, at the end of incubation period under elevated hydrostatic pressure the recovery of adenylyl cyclase activity to control levels was examined.

RESULTS

Cell viability did not change following exposure to elevated hydrostatic pressure for 6 hours. Cells subjected to elevated hydrostatic pressure demonstrated morphological differences characterised by a more rounded shape and a redistribution of actin stress fibres that was most prominent in lamina cribrosa astrocytes. A time dependent increase in basal adenylyl cyclase activity, and a decrease in maximum forskolin stimulated activity were observed in all cell lines following exposure to elevated hydrostatic pressure.

CONCLUSION

These observations demonstrate that cell lines from different ocular tissues are sensitive to changes in external pressure in vitro. They exhibit morphological and cytoskeletal changes as well as significant alterations of intracellular adenylyl cyclase activity following exposure to acute and sustained levels of elevated hydrostatic pressure of up to 6 hours' duration.

Antiplatelet effects of sodium nitroprusside in flowing human blood: studies under normoxic and hypoxic conditions

We explored the ability of sodium nitroprusside to modify adhesive and cohesive function of platelets in flowing blood, under normoxic and hypoxic conditions. Aliquots of both untreated and sodium nitroprusside-treated blood were prepared for studies of: (1) platelet aggregation in plasma; (2) erythrocyte deformability; (3) platelet interaction with damaged subendothelium, by using a well-defined perfusion system; and (4) blood gasometry in the perfused samples. Results showed that sodium nitroprusside-treated blood always showed a totally inhibited arachidonic acid-induced platelet aggregation in plasma, as well as significantly increased erythrocyte deformability (0.44+/-0.09 up to 0.66+/-0.05; p<0.05). However, treatment with sodium nitroprusside did not modify the pattern of platelet interaction with subendothelium (percentage of contact, adhesion, thrombus, and covered surface) with respect to untreated blood, under any of the shear rates used (300, 800, and 1800 seconds(-1)), although it significantly reduced the height of thrombi (9.8+/-0.4 vs. 8.3+/-0.4 microm; p<0.05). Hypoxic conditions did not have a noticeable effect in modifying antiplatelet effects of sodium nitroprusside. Additionally, the presence of sodium nitroprusside impaired the normal oxygenation of the blood during perfusion. pO2 in control untreated samples rose from 40.3+/-5.0 mm Hg perfusions to 100.4+/-12.5 mm Hg but remained at 66.3+/-6.3 mm Hg in sodium nitroprusside-treated blood (p<0.05). Our results did not show a significant effect of sodium nitroprusside in the modulation of platelet interaction with subendothelium. The marginal reduction in the thrombi height could be related to rheological interference of increased erythrocyte deformability.

Differential expression of neural cell adhesion molecule isoforms in normal and glaucomatous human optic nerve heads

Type 1B astrocytes of the human optic nerve head (ONH) constitutively express neural cell adhesion molecule (NCAM) in vivo and in vitro. Increased synthesis of NCAM has been detected in reactive astrocytes in the glaucomatous ONH of human donor eyes. Several NCAM isoforms are generated through alternate RNA splicing in tissue- and disease-specific patterns. In this study, we analyzed expression of NCAM isoforms in ONH of normal donors at different ages and in glaucoma. Total RNA was extracted from ONH of fetal, normal adult and glaucomatous eyes, and cultured human ONH astrocytes, fetal brain astrocytes and an astrocytoma cell line, for reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. To distinguish between NCAM 180 and 140 isoforms, exon-specific primer sets covering exons 13-19 were used. Isoform-specific riboprobes were used for in situ hybridization (ISH) in glaucomatous and in age-matched ONH. By RT-PCR, NCAM 140 was the predominant isoform in adult ONH as well as in all cultured cells. NCAM 180 mRNA was strongly expressed in glaucoma, whereas in normal adult tissues it was not detectable. ISH confirmed expression of NCAM in normal adult ONH and localized NCAM 140 mRNA to astrocytes. ISH demonstrated expression of NCAM 180 mRNA in reactive astrocytes in glaucomatous ONH. Our results demonstrate that the NCAM 180 isoform is induced in glaucoma. NCAM 180 may play a role in astrocyte interaction with extracellular matrix (ECM), vessels, axons and other astrocytes and, through its expanded cytoplasmic domain, serve as a signaling molecule for reactive astrocytes during remodeling of the ONH in glaucoma.

Assessment of potential thrombogenicity of coagulation factor IX concentrates in an in vitro model of human thrombogenesis

We have investigated the potential use of perfusion techniques in the evaluation of the thrombogenic profile of factor IX concentrates. Blood from healthy donors was anticoagulated with low molecular weight heparin and incubated with one of the following: (a) diluent (DIL); (b) a prothrombin complex concentrate (PCC); (c) an intermediate-purity concentrate (FIX/X); or (d) a high-purity concentrate (HPFIX). The thrombogenic potential was assessed as: (1) fibrin formation on subendothelium (Baumgartner's perfusion) and (2) prothrombin activation fragment 1+2 (F1+2, nM) determination. The percentage of fibrin deposition on the subendothelium was only significantly increased after incubation with PCC (62.0+/-3.6% vs. DIL 35.0+/-6.1%;p<0.05). None of the FIX concentrates modified platelet interaction versus control blood (DIL: 26.7+/-2.1%). F1+2 baseline values in anticoagulated blood were 0.6+/-0.1 nM. Preperfusion levels of F1+2 reached values of 4.4+/-0.1 nM for PCC and 5.4+/-0.1 nM for FIX/X. After perfusion, F1+2 values were 2.7+/-0.2 nM for DIL, 5.6+/-0.1 nM for PCC and FIX/X, and 3.3+/-0.2 nM for HPFIX. While measurement of F1+2 was influenced by residual contaminants present in the concentrates, the morphometric evaluation of fibrin deposition on perfused vascular surfaces could be more closely related to the net thrombogenic profile of each FIX preparation.

Transforming growth factor beta isoforms in human optic nerve heads

AIM

To determine if the isoforms of transforming growth factor beta (TGF-beta) are present in fetal, normal adult, and glaucomatous optic nerve heads.

METHODS

To localise cells synthesising TGF-beta, optic nerve heads were stained using antibodies to TGF-beta 1, TGF-beta 2, and TGF-beta 3. To demonstrate synthesis, human optic nerve heads from fetal, glaucomatous, and normal age matched subjects were explanted, cultured overnight, and the culture supernatant was assayed for the presence of TGF-beta 1 and TGF-beta 2 by bioassay. In addition, semiquantitative RT-PCR was performed to determine the gene expression pattern of TGF-beta 2.

RESULTS

Immunohistochemistry of glaucomatous samples revealed the presence of intense staining for TGF-beta 2 primarily in astrocytes, whereas TGF-beta 1 was localised to blood vessels. No TGF-beta 3 immunoreactivity was observed. There was little or no expression of TGF-beta in normal optic nerve heads. Optic nerve heads from glaucomatous eyes released 70-100-fold more TGF-beta 2 than normal age matched optic nerve heads. Fetal optic nerve heads released 90-100-fold more TGF-beta 2 than normal adult optic nerve heads. TGF-beta 1 was undetectable by bioassay in all samples tested. There was no apparent increase in TGF-beta 2 gene expression in glaucomatous and fetal eyes, suggesting post-transcriptional regulatory mechanisms.

CONCLUSIONS

These results demonstrate that TGF-beta 2 is produced in high levels in the fetal and glaucomatous optic nerve heads, perhaps by a mechanism of post-transcriptional regulation. TGF-beta may be important during development of the optic nerve head and, in glaucoma, TGF-beta 2 may be a mediator of astrocyte reactivation and extracellular matrix remodelling in the lamina cribrosa.

Enhanced tenascin expression associated with reactive astrocytes in human optic nerve heads with primary open angle glaucoma

Tenascin is a large extracellular matrix glycoprotein expressed in neural and non-neural tissues. In the central nervous system, tenascin is synthesized by astrocytes during development and wound healing, forming barriers and affecting neurite outgrowth. In this study we examined tenascin expression in optic nerve heads of normal and glaucomatous eyes and found that there is upregulation of tenascin mRNA and protein in reactive astrocytes from human glaucomatous optic nerve heads compared to normal age-matched controls. In the prelaminar region there was a band of tenascin immunoreactivity around the blood vessels of glaucomatous, but not in normal eyes. However, tenascin mRNA was only localized to astrocytes, suggesting that astrocytes are the cellular source of tenascin. In the lamina cribrosa, tenascin immunoreactivity and gene expression were localized to astrocytes in the cribriform plates and inside the nerve bundles. In the post-lamina region, tenascin immunoreactivity and gene expression were localized to astrocytes lining the pial septum immediately adjacent to the lamina cribrosa. In normal optic nerve heads, tenascin expression at the mRNA and protein levels was confined to clusters of astrocytes at the level of Bruch's membrane in the prelaminar optic nerve head. In glaucoma, enhanced expression of tenascin may be protective to the axons of the retinal ganglion cells by providing a barrier for humoral and/or blood-borne factors that may cause further neural damage. However, the precise role of tenascin in glaucomatous optic neuropathy is not yet elucidated.

Elastosis of the lamina cribrosa in glaucomatous optic neuropathy

The purpose of this study was to determine whether elastotic degeneration of the elastin component of the lamina cribrosa occurs in optic neuropathy associated with different types of glaucoma. Human optic nerve heads with primary open-angle, neovascular, chronic angle closure and pseudoexfoliation glaucoma, and with varying duration of disease were compared with age-matched normal eyes, using electron microscopy and immunogold labeling of elastin. The percent area occupied by immunogold-labeled elastin material was determined using a digital image analysis system. In all eyes with a history of glaucoma, elastosis was found in the lamina cribrosa and there was a significantly greater percentage of area occupied by elastin compared with age-matched control eyes (P<0.0001). Among the glaucomatous eyes, pseudoexfoliation glaucoma had the largest area of elastosis, followed by primary open-angle and secondary glaucoma (neovascular and chronic angle closure). In all glaucoma samples, large, confluent elastin aggregates of irregular and varied shapes (elastosis) were observed in the lamina cribrosa and insertion region. These results demonstrate that glaucomatous optic neuropathy is associated with elastosis of the lamina cribrosa, which may contribute to the changes in compliance of the optic nerve heads of glaucomatous eyes.

Cyclooxygenase-1 and cyclooxygenase-2 in the human optic nerve head

To investigate the hypothesis that eicosanoids act as cellular mediators in the optic nerve head of normals and of patients with glaucoma, we have determined the presence of the two cyclooxygenase (COX) isoforms in human tissue. Histological sections of optic nerve heads were studied by immunohistochemistry. Age matched normal donors were compared with eyes from glaucoma patients with moderate to severe nerve damage. Polyclonal antibodies to human COX-1 and COX-2 were localized with immunoperoxidase staining. Specific antibodies for vascular endothelia and microglia were also colocalized. In normal and glaucomatous eyes. COX-1 was localized exclusively to the prelaminar and lamina cribrosa regions of the optic nerve head. No staining for COX-1 was observed in the nerve fiber layer or the myelinated optic nerve. COX-1 was associated with the astrocytes of the glial columns and the cribriform plates, but not with the endothelia lining the capillaries. In glaucoma, more astrocytes appeared to be stained with antibody to COX-1 than in normals and staining was intensely perinuclear. There was no staining for COX-2 in normal tissue. A few COX-2 positive cells were found in the prelaminar, lamina cribrosa and postlaminar regions of the glaucomatous optic nerves. Positive staining for COX-2 was not associated with microglia. COX-1 is constitutively present in astrocytes that are localized exclusively to the prelaminar and lamina cribrosa regions of the human optic nerve head. Eicosanoids, synthesized by COX-1 in this tissue, may have a homeostatic and a neuroprotective role related to the axons of the retinal ganglion cells. The sparse presence of COX-2 in glaucomatous tissue probably reflects the lack of inflammation associated with glaucomatous optic neuropathy.

Astrocyte responses in human optic nerve head with primary open-angle glaucoma

PURPOSE

To identify and characterize astrocyte responses and reactivation in human optic nerve heads from patients with primary open-angle glaucoma.

METHODS

Fifteen optic nerve heads with primary open-angle glaucoma and 13 normal controls were fixed in 4% paraformaldehyde, paraffin embedded, and stained for immunofluorescence and immunoperoxidase. The antibodies used were against glial fibrillary acidic protein (GFAP) and against neural cell adhesion molecule (N-CAM).

RESULTS

Two subpopulations of type 1 astrocytes exist in the normal optic nerve. Type 1A astrocytes express only glial fibrillary acidic protein and type 1B express both glial fibrillary acidic protein and neural cell adhesion molecule. These are the major cell subpopulations in the lamina cribrosa and prelaminar regions. In primary open angle glaucoma, type 1B astrocytes in the prelaminar region showed increased immunoreactivity for glial fibrillary acidic protein and neural cell adhesion molecule, and cytoplasmic enlargement with thicker and longer cytoplasmic processes. At the level of the lamina cribrosa, type 1B astrocytes appeared round and the cell bodies were no longer in the cribriform plates but located in the nerve bundles. Type 1A astrocytes were not observed in the glaucomatous optic nerve head.

CONCLUSIONS

Astrocyte responses in primary open angle glaucoma may underlie cellular changes that lead to axonal damage and optic nerve head remodeling. These responses may have pathogenic significance for glaucomatous optic neuropathy.

Inhibition of fibrin deposition on the subendothelium by a monoclonal antibody to polymorphonuclear leukocyte integrin CD11b. Studies in a flow system

BACKGROUND AND OBJECTIVE

The development of prothrombotic and procoagulant states may be regulated by direct platelet-leukocyte contact mediated by membrane receptors. We have investigated the role of CD11b integrin in polymorphonuclear leukocytes (PMN) on fibrin formation and platelet reactivity with vascular subendothelium.

METHODS

Studies were carried out following a well-established perfusion model, employing either citrated blood, where fibrin formation is blocked, or blood anticoagulated with low molecular weight heparin, which allows thrombin and fibrin formation. Isolated PMN or platelets were treated with specific monoclonal antibodies to CD11b or to CD62P, respectively, and incorporated in reconstituted blood.

RESULTS

Treatment of PMN with anti-CD11b significantly decreased the percentage of surface covered with a thick layer (> 5 microns) of fibrin (34.8 +/- 3.3% vs 53.3 +/- 4.9% in control, p < 0.05); it also reduced the average height of fibrin layer and the number of adherent leukocytes (7.9 +/- 1.2 microns vs 10.6 +/- 1.4 microns in control, p < 0.05; and 87 +/- 8 PMN/mm2 vs 186 +/- 25 PMN/mm2 in control, p < 0.05) respectively. Treatment of PMN with CD11b did not significantly affect the attachment of platelets onto the subendothelium when using citrated blood, though a slight decrease in platelet adhesion was observed in the heparinized samples. Treatment of platelets with anti-CD62P did not significantly modify any of the parameters studied.

INTERPRETATION AND CONCLUSIONS

Our results indicate that PMN have a role in promoting fibrin deposition under flow conditions, through the participation of CD11b integrin. Under our experimental conditions, this effect does not seem to be influenced by CD62P expressed on activated platelets.

Expression of neural cell adhesion molecule (NCAM) characterizes a subpopulation of type 1 astrocytes in human optic nerve head

The human optic nerve contains a heterogeneous population of astrocytes. In situ, a specialized subpopulation of astrocytes was distinguished in the adult optic nerve head by expression of neural cell adhesion molecule (NCAM). To further study the biology of astrocytes, we have developed and characterized cells grown from explanted optic nerve heads and myelinated optic nerves as in vitro model systems. Second or third passage cells were processed for immunocytochemistry using antibodies against glial fibrillary acidic protein (GFAP) and cell surface epitopes: CD56/NCAM, HNK-1/NCAM, A2B5, and O4. Synthesis and gene expression of NCAM were characterized by Western blot analysis and RNase protection assay. Cells grown from myelinated optic nerves expressing GFAP, but not NCAM or A2B5, were identified as type 1A astrocytes, and cells expressing GFAP and A2B5, but not NCAM, were identified as type 2 astrocytes. Cells grown from explanted optic nerve head expressing GFAP, NCAM, and O4 were identified as type 1B astrocytes. Expression of NCAM by type 1B astrocytes may provide these cells with adhesion properties that allow them specialized responses in their microenvironment. Astrocytes from the lamina cribrosa may form a functional barrier to prevent myelination of the retina. In glaucoma, these astrocytes may be exposed to stresses due to fluctuation in intraocular pressure and therefore participate in the optic nerve changes associated with glaucomatous optic neuropathy.

Hyaluronic acid in the normal and glaucomatous optic nerve

Eighteen normal human eye-bank eyes (age: 18-81 years), five fetal eyes (16-24 weeks), 11 primary open-angle glaucoma (POAG) eyes (age: 76-89 years), and two Schnabel's cavernous optic atrophy eyes were examined using a biotinylated-hyaluronan binding protein to study the changes in the distribution of hyaluronic acid (HA) in the fetal, adult and glaucomatous optic nerve head. The vitreous body served as a positive control. Sections treated with Streptomyces hyaluronidase were used to confirm specificity. Monoclonal antibodies to myelin basic protein (MBP) and glial fibrillary acidic protein (GFAP) were used as additional controls. In fetal optic nerve, HA was localized in blood vessels, peripapillary sclera and the pial septae in the retrolaminar nerve. No staining was associated with axons. Staining for MBP was negative. In adults, HA was found surrounding the myelin sheaths in the retrolaminar nerve; staining decreased with age. In contrast, HA staining in myelinated peripheral nerves (e.g. ciliaries) remained unchanged with age. HA also was localized to the adventitia of arteries and veins throughout the posterior segment. Compared to age-matched normal eyes, HA staining was virtually absent around myelin sheaths of the retrolaminar nerve in POAG eyes. Similar changes were not found in other HA positive structures. In Schnabel's cavernous optic atrophy. HA was present in increased amount in the atrophic area, but virtually absent in the remaining retrolaminar nerve. HA staining was invariably positive in vitreous, and Streptomyces hyaluronidase treated sections were negative. In adults, staining of MBP was associated with the myelin sheath in the retrolaminar nerve. In contrast to HA, staining of MBP was unchanged with age and in POAG. In Schnabel's atrophy, MBP staining disappeared only in the atrophic area. HA in the retrolaminar optic nerve appears to be associate with the space-filling matrix between myelin sheaths. HA is not present in the axon bundles prior to myelination of the optic nerve. HA in the retrolaminar optic nerve appears to decrease with age and is further reduced in POAG; however, corresponding changes are not found in MBP or in peripheral nerves. Perhaps, decreased amounts of HA is related to a higher susceptibility to elevated intraocular pressure or to optic nerve atrophy. In Schnabel's cavernous optic atrophy, HA is present in increased amount only in the atrophic area while MBP is markedly decreased, suggesting in situ production of HA in areas of optic nerve atrophy.

Nitric oxide synthase in the human glaucomatous optic nerve head

OBJECTIVES

To investigate the hypothesis that nitric oxide contributes to neurotoxicity in the optic nerve heads of patients with primary open-angle glaucoma, we have determined the presence of the 3 isoforms of nitric oxide synthase (NOS) in the tissue.

METHODS

Histological sections of optic nerve heads from normal subjects and patients with glaucoma who have moderate to advanced nerve damage were studied by immunohistochemistry. Polyclonal antibodies to NOS-1, NOS-2, and NOS-3 were localized with immunoperoxidase staining.

RESULTS

In normal eyes, NOS-1 is sparsely present in astrocytes throughout the optic nerve head. In glaucomatous optic nerve heads, almost every astrocyte is positive for NOS-1. Nitric oxide synthase-1 immunoreactivity is abundantly present throughout the prelaminar region and the lamina cribrosa and is localized inside the diminished nerve fiber bundles. Nitric oxide synthase-2 is present in a few cells in the disorganized lamina cribrosa of the glaucomatous eye and is not present at all in normal tissue. Nitric oxide synthase-3 is present in normal eyes in the vascular endothelia of small blood vessels of the prelaminar region. In glaucomatous tissue, NOS-3 is present in astrocytes and in the vascular endothelia of large and small vessels.

CONCLUSIONS

The 3 isoforms of NOS are present in apparently increased amounts in the optic nerve head of patients with primary open-angle glaucoma. The increased presence of NOS-1 and the induction of NOS-2 in astrocytes of the lamina cribrosa suggest that the glaucomatous optic nerve head is exposed to excessive levels of nitric oxide, which may be neurodestructive, locally, to the axons of the retinal ganglion cells. Conversely, the increased presence of NOS-3 in vascular endothelia may be neuroprotective by causing vasodilation and increased blood flow in the tissue.

In vitro evaluation of the hemostatic effectiveness of non viable platelet preparations: studies with frozen-thawed, sonicated or lyophilized platelets

OBJECTIVES

Because of the limited life span of platelets in regular storage systems, we were interested in investigating the effects on hemostasis of nonliving platelet derivatives.

METHODS

We evaluated the effects of different platelet preparations on primary hemostasis in a well-established perfusion model. Studies were carried out with blood anticoagulated with low molecular weight heparin. Similar amounts of frozen-thawed, sonicated or lyophilized platelets were added to normal blood or to blood which had been experimentally depleted of platelets. Platelet interaction with the subendothelium and fibrin deposition were morphometrically evaluated.

RESULTS

Addition of nonviable platelet preparations to thrombocytopenic blood always promoted a statistically significant increase in the deposition of fibrin on the subendothelium, but only lyophilized platelets retained some ability to interact with the subendothelium. Flow cytometry studies demonstrated the presence of GPIb, GPIIIa and P-selectin on lyophilized platelets.

CONCLUSIONS

Preparations containing nonviable platelets may still retain some hemostatic properties.

Tropoelastin gene expression in optic nerve heads of normal and glaucomatous subjects

Elastic fibers are a major component of the extracellular matrix in the optic nerve head (ONH) and undergo marked morphological changes during primary open angle glaucoma (POAG). Previous findings indicated that there is reactivation of tropoelastin mRNA synthesis in glaucoma. In this study, we sought to determine the alternative splicing pattern of tropoelastin in the human optic nerve head and in cultured laminar astrocytes. Furthermore, we compared the alternative splicing pattern of normal elastogenesis with that of reactivation of elastin synthesis in patients with primary open angle glaucoma. Our results demonstrate that exons 23 and 32 of tropoelastin are alternatively spliced in the normal ONH as well as in tissue from glaucomatous patients. There are no qualitative differences. We also demonstrated that astrocytes from the ONH synthesize tropoelastin in vitro. In conclusion, we have demonstrated a tropoelastin alternative splicing pattern in the human optic nerve head and laminar astrocytes. Abnormalities in elastic fibers in the ONH of patients with POAG are not due to an aberrant splice variant of tropoelastin. Astrocytes grown from ONH explants may serve as an in vitro model to study extracellular matrix changes in glaucoma.

Heterogeneity of astrocytes in human optic nerve head

Previous studies demonstrated regional differences in the synthesis of extracellular matrix by astrocytes during optic nerve head (ONH) maturation and in glaucomatous optic neuropathy, suggesting heterogeneity of astrocytes. To characterize different types of glial cells in human fetal and adult ONH, we used a variety of neural cell markers such as HNK-1/N-CAM, A2B5, galactocerebroside (GalC), myelin basic protein (MBP), and glial fibrillary acidic protein (GFAP). Cryostat or paraffin sections were prepared from fetal (16-25 weeks) and mature (8 months to 75 years old) ONH and processed for standard single/double immunocytochemistry. Two subpopulations of type 7 astrocytes were present in the mature prelaminar and laminar regions. Glial cells expressing only GFAP were identified as type 1A astrocytes at the edges of the cribriform plates. Cells forming the glial columns and lining the cribriform plates expressed both GFAP and HNK-1/N-CAM and were identified as type 1B astrocytes. In the myelinated nerve, type 1A astrocytes form the glial limiting membrane. Cells labeled with GFAP and A2B5 were identified as type 2 astrocytes, and GFAP-negative cells labeled with GalC, MBP, and HNK-1/N-CAM were identified as oligodendrocytes. In fetal ONH, all glial cells expressed HNK-1/N-CAM. In older fetal ONH, some glial cells also expressed GFAP. No type 2 astrocytes or oligodendrocytes were present in the fetal ONH. In conclusion, at least two subpopulations of type 1 astrocytes exist in human ONH: Type 1A astrocytes may serve as structural support for axons; type 1B astrocytes, which retain the developmental neural marker HNK-1/N-CAM, may have a more complex function by interfacing between blood vessels and other connective tissue surfaces. These findings demonstrate the heterogeneity of astrocytes in the human ONH and suggest differential regional responses to changes in their microenvironment.

ONTRAK TESTCUP: a novel, on-site, multi-analyte screen for the detection of abused drugs

We developed a rapid, sensitive, and simple-to-use multi-analyte diagnostic device for the detection of drugs of abuse in urine: the ONTRAK TESTCUP. No sample or reagent handling is necessary with this device, and the device also serves as the sample collection cup. The TESTCUP contains immunochromatographic reagents that qualitatively and simultaneously detect the presence of benzoylecgonine, morphine, and cannabinoids (delta9-tetrahydrocannabinol [THC] in urine. It is based on the principle of competition between the drug in the sample and membrane- immobilized drug conjugate for antidrug antibodies coated on blue-dyed microparticles. Each drug assay has its own strip, which contains an antibody specific to benzoylecgonine, morphine, or THC. A sample is collected in the TESTCUP, a lid is placed on it, and a chamber at the top of the cup is filled with urine by inverting the cup for 5 s. Urine proceeds down immunochromatographic strips, and the assays are developed. In approximately 3-5 min, the Test Valid bars appear, a decal is removed from the detection window, and the results are interpreted. The appearance of a colored bar at the detection window for each drug indicates a negative result. The absence of color in any specific drug detection window indicates a positive result for that drug. If a positive result is obtained, the same device (cup) can be used for gas chromatographic-mass spectrometric (GC-MS) confirmation. When the precision of the TESTCUP was evaluated, the results obtained were as follows: for urine controls containing drug at 50% of its cutoff concentration, the results were greater than or equal to 96, 98, and 96% negative for benzoylecgonine, morphine, and THC, respectively; for urine controls containing drug at 120% of its cutoff concentration, the results were greater than or equal to 97, 100, and 98% positive for benzoylecgonine, morphine, and THC, respectively. The correlations of clinical sample results using the TESTCUP versus results by GC-MS and the ONTRAK and OnLine assays were assessed. There was 100% agreement between samples prescreened positive by GC-MS and positive by TESTCUP for all three assays. There was 100% agreement between TESTCUP and ONTRAK results and between TESTCUP and OnLine results when testing clinical samples positive and negative for cocaine (benzoylecgonine) or THC. Greater than 99% agreement was observed between TESTCUP and ONTRAK results and between TESTCUP and OnLine results when testing clinical samples positive and negative for morphine. The cross-reactivity of the TESTCUP assay to related drugs and drug metabolites was also determined, and the results were similar to those of the ONTRAK and OnLine assays.

Expression of muscarinic receptor subtype mRNA in the human ciliary muscle

PURPOSE

To investigate the expression of the muscarinic receptor (mAChR) subtypes (m1, m2, m3, m4, and m5) in the human ciliary muscle.

METHODS

cDNA probes specific for the m1 to m5 subtypes were used to characterize the expression of subtype-specific mRNAs by in situ hybridization and Northern blot analysis on a cell line derived from human ciliary muscle tissue (H7CM), sectioned tissue from four donors, and fresh human ciliary muscle tissue from three donors.

RESULTS

Messenger RNA for m2, m3, and m5 was detected in situ hybridization and Northern blot analysis in the H7CM cell line and in human ciliary muscle tissue from the donors. In human ciliary muscle tissues, the expression of mRNA of the m2 and m3 subtypes was more prominent in the circular portion than in the longitudinal portion. In contrast, mRNA for the m5 subtype was greater in the longitudinal portion than in the circular portion. Additionally, Northern blot analysis showed that m1 and m4 were expressed in ciliary muscle tissue.

CONCLUSION

These studies show that the human ciliary muscle definitely expresses the mRNA of subtypes m2, m3, and m5, and may also express the mRNA of m1 and m4. Although the expression of mRNA for the m2, m3, and m5 subtypes differed between the circular and longitudinal portions of the ciliary muscle, the strong expression of all three subtypes of muscarinic receptors by both portions demonstrates that the differential distribution of muscarinic subtypes probably is not responsible for the dissociation between outflow facility and accommodation that can occur under certain conditions.

Elastosis of the lamina cribrosa in pseudoexfoliation syndrome with glaucoma

BACKGROUND

Pseudoexfoliation syndrome is characterized by the presence of glycoprotein fibers in ocular and extraocular tissues, and often is associated with glaucoma. Pseudoexfoliation material may be associated closely with elastic microfibrillar-associated glycoprotein as well as elastin.

METHODS

Four optic nerve heads of two patients with pseudoexfoliation syndrome and glaucoma were examined using electron microscopy and immunogold detection of elastin. Optic nerve heads from healthy age-matched individuals and patients with primary open-angle glaucoma were used for comparisons.

RESULTS

In all eyes with pseudoexfoliation and glaucoma, there was marked and widespread elastosis in the connective tissue of the lamina cribrosa. Elastotic fibers appeared as large and irregular aggregates of electron-dense material labeled with anti-elastin antibody. Abundant microfibrils were interspersed in the elastotic aggregates, whereas no typical pseudoexfoliation fibers were observed. In contrast, there were less elastotic fibers in the lamina cribrosa from patients with primary open-angle glaucoma compared with pseudoexfoliation glaucoma. Other changes of extracellular matrix were similar to those observed in primary open-angle glaucoma: decreases in collagen fiber density, presence of basement membranes not associated with cell surfaces, and abundant bundles of microfibrils not labeled with elastin antibody. The elastic fibers appeared normal in other locations within the optic nerves of patients with pseudoexfoliation glaucoma, including in the pial septa and blood vessels of the retrolaminar myelinated optic nerve.

CONCLUSION

The authors' findings demonstrate marked and site-specific elastosis in the lamina cribrosa of patients with pseudoexfoliation syndrome with glaucoma, suggesting an abnormal regulation of elastin synthesis and/or degradation in the optic nerve of patients with this disease.

Collagen type IV gene expression in human optic nerve heads with primary open angle glaucoma

Previous studies have demonstrated proliferation of basement membranes in the optic nerve head in primary open angle glaucoma (POAG). We used in situ hybridization (ISH) of a radiolabeled riboprobe specific for human collagen IV, a ubiquitous component of basement membranes, to identify cells actively synthesizing basement membranes in the optic nerve head in POAG. In addition, to detect and further characterize the collagen IV mRNA transcripts, we used reverse transcriptase-polymerase chain reaction (RT-PCR) in total RNA extracted from individual optic nerve heads with POAG and from age-matched normal controls. ISH results demonstrate that, in POAG, numerous astrocytes in the prelaminar region expressed collagen IV mRNA. Lamina cribrosa cells and astrocytes in the compressed lamina cribrosa hybridized the probe. Few astrocytes and lamina cribrosa cells hybridized the probe in the optic nerve head of normal age-matched controls. RT-PCR products for collagen IV and for glyceraldehyde-3-dehydrogenase (G3PDH), a reference gene, were detected by agarose electrophoresis as single bands of the expected sizes and positively identified by Southern hybridization using specific cDNA probes in normal and POAG samples. No additional products (bands) were observed in RT-PCR experiments, indicating that there was no genomic DNA contamination in the total RNA extract. The lack of additional bands suggests that, at least in the ten samples used in this study, there were no alternatively spliced RNA products in any of the amplified sequences. Semi-quantitative analyses using densitometry showed a two-fold increase in collagen type IV PCR present in POAG samples. No differences were detected in levels of G3PDH PCR products between POAG and normal samples. This investigation provides evidence of increased biosynthesis of collagen type IV at the mRNA level in optic nerve heads with POAG. Whether this phenomenon represents a response to elevated intraocular pressure or a reparative mechanism to the loss of axons remains to be determined.

Activation of elastin mRNA expression in human optic nerve heads with primary open-angle glaucoma

Elastin is the major protein of elastic fibers and is responsible for the elastic recoil. Elastic fibers are a major component of the extracellular matrix in the human lamina cribrosa and undergo marked changes in primary open-angle glaucoma. Ultrastructural and immunocytochemical analysis demonstrated fragmentation of elastic fibers, accumulation of nonfibrillar elastic material, and bundles of microfibrils in the core of the cribriform plates in primary open-angle glaucoma. The changes in elastic fibers increased with the progression of the disease and strongly suggested abnormal biosynthesis, degradation of elastic fibers, or both. In this study, we used in situ hybridization and reverse transcriptase-polymerase chain reaction to localize and detect expression of elastin messenger RNA (mRNA) in human optic nerve heads with primary open-angle glaucoma and age-matched normal controls. The major finding of this study is the demonstration of elastin mRNA in the lamina cribrosa cells of optic nerve heads with primary open-angle glaucoma and the absence of this message in normal donors. Several studies have demonstrated a concordance between levels of elastin and relative levels of elastin mRNA. Our findings indicate de novo synthesis of elastin in the compressed lamina cribrosa in primary open-angle glaucoma. Synthesis of abnormal elastic fibers must alter the mechanical properties of the lamina cribrosa and may lead to compression, remodeling, and rearrangement of the cribriform plates characteristic of glaucomatous cupping.

Localization of collagen type III mRNA in normal human optic nerve heads

Previous studies using immunocytochemistry and electron microscopy have localized collagen type III (CIII) in the human optic nerve head (ONH). CIII is present in the core of the cribriform plates of the lamina cribrosa and increases with age. In this study, in situ hybridization was used to localize mRNA for CIII in specific cells in human fetal and adult ONH to determine its cellular origin and to provide temporal and regional information on the synthesis of CIII in the ONH. Human ONH from donors with no history of eye disease (16-24 weeks gestation and 6-75 years) were fixed, embedded and sectioned serially. Sections were hybridized with antisense riboprobe for CIII and controls with sense riboprobe and processed for ISH. Immunoperoxidase staining with antibodies against GFAP and von Willebrand factor was used to detect astrocytes and vascular endothelial cells respectively. Fetal ONH: CIII mRNA was localized in most blood vessels throughout the ONH in sections hybridized with antisense probe. The label was localized to endothelial cells of small vessels. Endothelial cells of central retinal vessels were not labeled. In the lamina cribrosa, CIII mRNA was localized to small vessels, but not to astrocytes. Fibroblasts of the peripapillary sclera were labelled with antisense probe. Young-Adult ONH: In the cribriform plates, lamina cribrosa cells hybridized the probe at all ages. Few astrocytes hybridized the probe. Some endothelial cells of small vessels were also labeled. In the insertion region, most vessels were labeled in young ONH, but very few, if any, in old adults. The apparent intensity of hybridization signal associated with blood vessels in adult ONH is markedly reduced with age. No hybridization was observed inside of nerve bundles consistent with the absence of mRNA inside axon and CIII in this location. Localization of mRNA for CIII to blood vessels in fetal lamina cribrosa suggests a vascular origin for CIII in the plates, and perhaps, for lamina cribrosa cells. In young and old lamina cribrosa, localization of CIII mRNA suggests lifelong synthesis of this protein in agreement with age-related increase of CIII in this tissue.

Glaucoma: changes in extracellular matrix in the optic nerve head

Primary open angle glaucoma (POAG), the most common form of glaucoma, is characterized by irreversible loss of axons from the optic nerve. The site of damage to the axons is at the level of the lamina cribrosa in the optic nerve head. It has been hypothesized that structural and biochemical abnormalities in the extracellular matrix (ECM) of the lamina cribrosa underlie the progressive compressive and remodelling of this connective tissue in glaucoma. In this review, we present evidence of specific changes in collagen and elastic fibers, major ECM components in the lamina cribrosa of glaucomatous eyes.

Collagen type I mRNA levels in cultured human lamina cribrosa cells: effects of elevated hydrostatic pressure

In primary open-angle glaucoma, elevated intraocular pressure is associated with distortion and reorganization of the connective tissue plates of the lamina cribrosa. We have previously postulated that the resident cells of the lamina cribrosa may respond to elevated intraocular pressure by altering the biosynthesis or degradation of extracellular matrix. To determine the response of lamina cribrosa cells to increased pressure, we have compared cultures of human lamina cribrosa cells, from five individuals, maintained under control and pressurized conditions in vitro. Cells from third to fifth passage cultures of human lamina cribrosa subjected to elevated hydrostatic pressure (50 mm Hg) for 7 days changed shape from flat and polygonal to elongated, synthesized and secreted increased amounts of collagen type I as shown by immunofluorescent localization, and exhibited increased mRNA levels of collagen type I (199 +/- 36% of control) (mean +/- S.D.), as determined by slot-blot hybridization. In contrast, beta-actin mRNA levels were unchanged, indicating that the effects of elevated pressure are probably relatively selective. Our data indicate that elevated pressure increases the synthesis of collagen Type I by human lamina cribrosa cells in vitro. In vivo, lamina cribrosa cells may react to changes in their environment by modulating, specifically, changes in the mRNA levels, production, and secretion of extracellular matrix macromolecules. The relationship of these changes in extracellular matrix to those observed in glaucoma remains to be determined.

Ultrastructural immunocytochemical analysis of elastin in the human lamina cribrosa. Changes in elastic fibers in primary open-angle glaucoma

The elastic fiber consists of several components: a central core of alpha-elastin and a microfibrillar sheath containing three components: fibrillin, microfibril-associated glycoprotein, and a 35-kD protein with amine oxidase activity. Elastin is a major component of the elastic fibers of the extracellular matrix (ECM) of the lamina cribrosa, and elastic fibers undergo marked changes in primary open-angle glaucoma (POAG). These changes, as demonstrated previously, include loss and fragmentation of elastic fibers at the bottom of the glaucomatous cup and disorganization in the peripheral walls of the cup. The author characterized the changes in elastic fibers with age and in POAG at the ultrastructural level, using colloidal gold immunostaining and anti-human alpha-elastin antibody. In fetal eyes, there was no detectable elastin in the ECM of the lamina cribrosa. In infant eyes, elastin was present in microfibrillar aggregates in the core of the plates. In young adults, thin elastic fibers were present that ran longitudinally in the core of the plates. With age, elastic fibers become thicker, tubular, and surrounded by densely packed collagen fibers. In mild POAG, tubular elastic fibers no longer were identifiable. Fragments of elastic fibers and microfibrillar aggregates stained positively for elastin suggested new synthesis of elastin that was not organized into tubular elastic fibers. In advanced POAG, masses of nonfibrillar elastin-positive material had a spotted appearance. Throughout the cribriform plates, there was a loss of collagen fibers, proliferation of basement membranes, and bundles of elastin-negative microfibrils not associated with collagen or elastic fibers. The progression of marked changes in elastic fibers and the disorganization of the ECM of the lamina cribrosa was associated with the loss of function and continuous remodeling of the optic nerve head in POAG.

Localization of collagen types I and IV mRNAs in human optic nerve head by in situ hybridization

Using in situ hybridization, individual cells expressing mRNAs for collagen types I and IV were localized in fixed-tissue sections of adult and fetal human optic nerve heads. Astroglial cells lining the cribriform plates and cells inside the cribriform plates of the lamina cribrosa had mRNA for collagen type IV. Cells in the glial columns, pial septa, and vascular wall also contained mRNA collagen type IV. Collagen type I mRNA was expressed by cells of the cribriform plates of the lamina cribrosa of adults. Few cells in the glial columns, pial septa, and blood vessels had mRNA for collagen type I. Scleral fibroblasts contained mRNA for collagen type I. These results indicated that the expression of mRNA for both collagen types I and IV paralleled the localization of these extracellular matrix proteins in the optic nerve head and suggested that both collagen types were synthesized in this tissue throughout life.

Changes in the extracellular matrix of the human optic nerve head in primary open-angle glaucoma

Using immunofluorescent staining, we were able to characterize the changes in composition and distribution of the macromolecules making up the extracellular matrix of the lamina cribrosa of the glaucomatous human optic nerve head. In tissue adjacent to the glaucomatous cups, there was marked disorganization and loss of fibers of elastin within the cores of the cribriform plates. Collagen type VI, normally sparse, increased in quantity considerably throughout the lamina cribrosa in glaucomatous eyes with all degrees of damage. Collagen type IV and other basement membrane macromolecules appeared to extend into nerve bundles, presumably filling in spaces previously occupied by nerves. There was no appreciable change in the postlaminar region, which indicates the specificity of the extracellular matrix changes in the lamina cribrosa. Our results indicate that changes in the extracellular matrix play an important role in the progression of the glaucomatous process and may be a causative agent of the disease.