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

Three-Dimensional Bioprinting of Astrocytes and Endothelial Cells to Direct Retinal Axon Growth and Vascularization

Retinal organoids (ROs) are currently used to study retinal development and diseases but cannot model glaucoma because they fail to form a nerve fiber layer (NFL) and optic nerve (ON). Utilizing three-dimensional bioprinting, ON head astrocytes (ONHAs) and vascular endothelial cells, both of which contribute to NFL development in vivo but are absent in ROs, were positioned at the center of scaffolds seeded with retinal ganglion cells (RGCs). In experiments using ONHAs isolated from developing retinas, polarization of RGC neurite growth increased by 43% while ONHA from adult retinas or astrocytes from the developing peripheral retina or developing cortex did not increase polarization above controls. Furthermore, RGC-seeded scaffolds increased both the number and rate of ONHAs migrating out from the printed center compared to scaffolds lacking RGCs, mimicking the migration pattern observed during retinal development. Finally, in scaffolds containing both ONHAs and endothelial cells, the endothelial cells preferentially migrate on and only form vascular tube structures on scaffolds also containing RGCs. These results suggest that recreating the developmental organization of the retina can recapitulate the mechanism of NFL development and retinal vascularization in vitro. This step is not only necessary for the development of retinal models of glaucoma but has the potential for translation to other parts of the central nervous system.

Whole-exome sequencing identifies multiple pathogenic variants in a large South Indian family with primary open-angle glaucoma

Purpose:

To identify the pathogenic variants associated with primary open-angle glaucoma (POAG) using whole-exome sequencing (WES) data of a large South Indian family.

Methods:

We recruited a large five-generation South Indian family (n = 84) with a positive family history of POAG (n = 19). All study participants had a comprehensive ocular evaluation. We performed WES for 16 samples (nine POAG and seven unaffected controls) since Sanger sequencing of the POAG candidate genes (MYOC, OPTN, and TBK1) showed no genetic variation. We used an in-house pipeline for prioritizing the pathogenic variants based on their segregation among the POAG individual.

Results:

We identified one novel and five low-frequency pathogenic variants with consistent co-segregation in all affected individuals. The variant c.G3719A in RPGR-interacting domain of RPGRIP1 that segregated heterozygously with the six POAG cases is distinct from variants causing photoreceptor dystrophies, reported affecting the RPGR protein complex signaling in primary cilia. The cilia in trabecular meshwork (TM) cells has been reported to mediate the intraocular pressure (IOP) sensation. Furthermore, we identified a novel c.A1295G variant in Rho guanine nucleotide exchange factors Gene 40 (ARHGEF40) and a likely pathogenic variant in the RPGR gene, suggesting that they may alter the RhoA activity essential for IOP regulation.

Conclusion:

Our study supports that low-frequency pathogenic variants in multiple genes and pathways probably affect Primary Open Angle Glaucoma’s pathogenesis in the large South Indian family. Furthermore, it requires larger case-controls to perform family-based association tests and to strengthen our analysis.

Isolation and characterization of human optic nerve head astrocytes and lamina cribrosa cells

The lamina cribrosa is the initial site of glaucomatous injury. Pathological changes to the lamina cribrosa include posterior displacement of the lamina cribrosa, loss of trophic support, and remodeling of the extracellular matrix. Optic nerve head (ONH) astrocytes and lamina cribrosa cells synthesize extracellular matrix proteins to support and maintain the lamina cribrosa under physiological conditions. During glaucoma, these cells respond to mechanical strain and other stimuli, which leads to pathological remodeling of the ONH. Although ONH astrocytes and lamina cribrosa cells have been previously cultured, there is no well-accepted, straightforward technique to isolate both cell types from a single dissected human ONH. To better understand the pathophysiology of glaucoma, we obtained and cultured lamina cribrosa explants from human donor eyes. Initially, cells that grew out from the explant were ONH astrocytes and lamina cribrosa cells. Using a specialized medium, we isolated pure populations of lamina cribrosa cells and ONH astrocytes. ONH astrocytes expressed glial fibrillary acidic protein (GFAP). Lamina cribrosa cells expressed alpha-smooth muscle actin (α-SMA), but were negative for GFAP. This method of ONH cell isolation and cell-culture will provide a technique to better understand the molecular and cell-specific changes in glaucomatous damage to the ONH.

A neuroglia-based interpretation of glaucomatous neuroretinal rim thinning in the optic nerve head

Neuroretinal rim thinning (NRR) is a characteristic glaucomatous optic disc change. However, the precise mechanism of the rim thinning has not been completely elucidated. This review focuses on the structural role of the glioarchitecture in the formation of the glaucomatous NRR thinning. The NRR is a glia-framed structure, with honeycomb geometry and mechanically reinforced astrocyte processes along the transverse plane. When neural damage selectively involves the neuron and spares the glia, the gross structure of the tissue is preserved. The disorganization and loss of the glioarchitecture are the two hallmarks of optic nerve head (ONH) remodeling in glaucoma that leads to the thinning of NRR tissue upon axonal loss. This is in contrast to most non-glaucomatous optic neuropathies with optic disc pallor where hypertrophy of the glioarchitecture is associated with the seemingly absent optic disc cupping. Arteritic anterior ischemic optic neuropathy is an exception where pan-necrosis of ONH tissue leads to NRR thinning. Milder ischemia indicates selective neuronal loss that spares glia in non-arteritic anterior ischemic optic neuropathy. The biological reason is the heterogeneous glial response determined by the site, type, and severity of the injury. The neuroglial interpretation explains how the cellular changes underlie the clinical findings. Updated understandings on glial responses illustrate the mechanical, microenvironmental, and microglial modulation of activated astrocytes in glaucoma. Findings relevant to the possible mechanism of the astrocyte death in advanced glaucoma are also emerging. Ultimately, a better understanding of glaucomatous glial response may lead to glia-targeting neuroprotection in the future.

Major review: Molecular genetics of primary open-angle glaucoma

Glaucoma is a leading cause of irreversible blindness worldwide. Primary open-angle glaucoma (POAG), the most common type, is a complex inherited disorder that is characterized by progressive retinal ganglion cell death, optic nerve head excavation, and visual field loss. The discovery of a large, and growing, number of genetic and chromosomal loci has been shown to contribute to POAG risk, which carry implications for disease pathogenesis. Differential gene expression analyses in glaucoma-affected tissues as well as animal models of POAG are enhancing our mechanistic understanding in this common, blinding disorder. In this review we summarize recent developments in POAG genetics and molecular genetics research.

Investigating the potential immune role of fish NCAMs: Molecular cloning and expression analysis in mandarin fish

The immune role of NCAMs has been revealed in mammals, yet there is no such report in fish. Hence, we analyzed the molecular characterizations and immune-associated expression patterns of NCAMs in mandarin fish. Three NCAM members, named mfNCAM1a, mfNCAM1b and mfNCAM2, were identified. Among the cDNA sequences of mfNCAMs, AU-rich elements in the 3' UTRs of mfNCAM1b and mfNCAM2 as well as VASE sequences in the fourth Ig-like domain-encoding regions of mfNCAM1a and mfNCAM1b were discovered. Moreover, the syntenic analysis suggested that the duplication of NCAM1 is fish-specific. At mRNA and protein levels, the expression analyses revealed that mfNCAMs existed in both systemic and mucosal immune tissues, and located within lymphoid cells. Upon stimulated either by LPS or poly I:C, the expression level of mfNCAM1a was significantly up-regulated in head kidney, spleen, liver, and gut, whereas mfNCAM1b only in head kidney and liver, and mfNCAM2 only in liver. Additionally, the cells coexpressed mfNCAM1 and mfNCCRP-1 might imply the equivalents to mammalian NK cells. Our finding firstly demonstrates the member-specific immune-related tissue expression pattern and immune activity for fish NCAMs. Current data indicate that mfNCAM2 has little immune activity, while the immune activity of mfNCAM1a exists in more tissues than mfNCAM1b, and mfNCAM1a may tend to respond more actively to viral while mfNCAM1b to bacterial stimulants. Additionally, NCAM1b should be a fish-specific member with unique immune function, judging from its different expression pattern, immune activity as well as phylogenetic relationship to mfNCAM1a.

Immunoproteomic analysis of potential serum biomarker candidates in human glaucoma

PURPOSE

Evidence supporting the immune system involvement in glaucoma includes increased titers of serum antibodies to retina and optic nerve proteins, although their pathogenic importance remains unclear. This study using an antibody-based proteomics approach aimed to identify disease-related antigens as candidate biomarkers of glaucoma.

METHODS

Serum samples were collected from 111 patients with primary open-angle glaucoma and an age-matched control group of 49 healthy subjects without glaucoma. For high-throughput characterization of antigens, serum IgG was eluted from five randomly selected glaucomatous samples and analyzed by linear ion trap mass spectrometry (LC-MS/MS). Serum titers of selected biomarker candidates were then measured by specific ELISAs in the whole sample pool (including an additional control group of diabetic retinopathy).

RESULTS

LC-MS/MS analysis of IgG elutes revealed a complex panel of proteins, including those detectable only in glaucomatous samples. Interestingly, many of these antigens corresponded to upregulated retinal proteins previously identified in glaucomatous donors (or that exhibited increased methionine oxidation). Moreover, additional analysis detected a greater immunoreactivity of the patient sera to glaucomatous retinal proteins (or to oxidatively stressed cell culture proteins), thereby suggesting the importance of disease-related protein modifications in autoantibody production/reactivity. As a narrowing-down strategy for selection of initial biomarker candidates, we determined the serum proteins overlapping with the retinal proteins known to be up-regulated in glaucoma. Four of the selected 10 candidates (AIF, cyclic AMP-responsive element binding protein, ephrin type-A receptor, and huntingtin) exhibited higher ELISA titers in the glaucomatous sera.

CONCLUSIONS

A number of serum proteins identified by this immunoproteomic study of human glaucoma may represent diseased tissue-related antigens and serve as candidate biomarkers of glaucoma.

State-dependent changes in the expression levels of NCAM-140 and L1 in the peripheral blood cells of bipolar disorders, but not in the major depressive disorders

Recent postmortem brain and imaging studies provide evidence for disturbances of structural and synaptic plasticity in patients with mood disorders. Several lines of evidence suggest that the cell adhesion molecules (CAMs), neural cell adhesion molecules (NCAM) and L1, play important roles in both structural and synaptic plasticity. Although postmortem brain studies have indicated altered expression levels of NCAM and L1, it is still unclear whether these changes are state- or trait-dependent. In this study, the mRNA levels for various CAMs, including NCAM and L1, were measured using quantitative real-time PCR in peripheral blood cells of major depressive disorder patients, bipolar disorder patients and normal healthy subjects. Reduced expression levels of NCAM-140 mRNA were observed in bipolar disorder patients in a current depressive state. In contrast, L1 mRNA levels were increased in bipolar disorder patients in a current depressive state. NCAM-140 and L1 mRNA levels were not changed in bipolar disorder patients in a remissive state, or in major depressive disorder patients. In addition, there were no significant changes in the expression levels of intercellular adhesion molecule -1, vascular cell adhesion molecule -1, E-cadherin, or integrin alphaD among healthy controls, major depressive or bipolar disorder patients. Our results suggest that the reciprocal alteration in the expression of NCAM-140 and L1 mRNAs could be state-dependent and associated with the pathophysiology of bipolar disorder.

Neural cell adhesion molecule (NCAM) isoform expression is associated with neuroblastoma differentiation status

BACKGROUND

NCAM is a member of the immunoglobulin superfamily of cell adhesion molecules. While highly expressed on neuroblastoma cells, the relative contribution of the three major NCAM isoforms (120, 140, and 180 kDa) to neuroblastoma biology has not been investigated.

METHODS

NCAM protein expression was measured in a neuroblastic tumor tissue microarray (N = 185) by immunohistochemistry. Relative expression of NCAM mRNA isoforms was measured in a panel of 24 human neuroblastomas and compared to fetal and adult human brain using real-time quantitative PCR and Western blot analysis. Associations with clinical and tumor biological co-variates were performed.

RESULTS

NCAM protein was detected on all neuroblastic tumors and was highly expressed in all but 7/167 cases. The mRNA species predicted to encode the 120 kDa protein species was the most abundant isoform in adult brain, ganglioneuromas and ganglioneuroblastomas (P = 0.0007), but the mRNA predicted to encode the 180 kDa species was predominant in neuroblastomas (P = 0.043). Microdissected ganglion and neuroblast cells from human primary tumors confirmed these findings.

CONCLUSION

Ganglioneuromas and ganglioneuroblastomas express the adhesive 120 kDa NCAM isoform, while neuroblastomas preferentially express the 180 kDa isoform classically involved in cell motility. These data suggest a mechanism for the enhanced metastatic potential of undifferentiated neuroblastomas.

Alteration of serum and tumoral neural cell adhesion molecule (NCAM) isoforms in patients with brain tumors

The neural cell adhesion molecule (NCAM) is involved in the intercellular junctions of neurons and glial cells. We investigated its relevance as a biomarker in gliomas which main characteristic is their high invasiveness. We studied by Western blot the pattern of serum NCAM bands in patients with gliomas (n = 34), with brain metastasis of different primary cancers (n = 27) and with benign brain tumors (n = 22)] compared with healthy controls (n = 69). For densitometric analysis NCAM bands > or = 130 kDa (HMW) and <130 kDa (LMW) were clustered. We observed that glioma patients presented higher NCAM HMW and lower NCAM LMW levels than control subjects (P < 0.01). A similar pattern was found in patients with brain metastasis or brain benign tumors, suggesting that the pattern of serum NCAM bands would be useful to detect brain tumor pathology. On the other hand, serum NCAM expression was not associated with the main clinicopathological features of gliomas, including overall survival. Interestingly, we found that 9/12 patients with glioma showed a significant decrease in NCAM HMW/LMW ratio between 1-3 months after successful tumor removal. Thus, serum NCAM could be a useful marker for monitoring treatment.NCAM expression was also analyzed at tissular level in 59 glioma sections from paraffined tumors. We observed that NCAM immunostaining was inversely correlated with the histological grade of malignancy, remaining this association in a multivariate analysis. Besides, loss of NCAM staining was significantly associated with bad prognosis in an univariate analysis.

[Effects of Yiqi Huayu Recipe on neural cell adhesion molecule in rats with lumbar nerve root compression]

OBJECTIVE

To study the effects of Yiqi Huayu Recipe on neural cell adhesion molecule (N-CAM) in neuromuscular junctions during nerve regeneration in rats with lumbar nerve root compression.

METHODS

The rats with lumbar nerve root compression were given Yiqi Huayu Recipe for 10, 20 and 30 days respectively. The distribution of N-CAM in neuromuscular junctions of soleus muscle in rats was examined with immunohistochemical method and confocal laser scanning microscopy technique. The acetylcholine receptor (AChR) was visualized with fluorescein-conjugated alpha-bungarotoxin (alpha-BTX). The overlap areas of N-CAM and AChR sites were measured with NIH image technique.

RESULTS

The aggregates, sprouts and extensions of N-CAM in the neuromuscular junctions and the overlap areas of N-CAM and AChR sites in the Yiqi Huayu Recipe-treated group were all better improved than those in the untreated group.

CONCLUSION

The expression of N-CAM is regulated according to the state of innervation for muscles. Yiqi Huayu Recipe may accelerate this nerve regeneration process.

Functional dichotomy: glutathione and vitamin E in homeostasis relevant to primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is a complex chronic neurological disease that can result in blindness. The goal of understanding the aetiology of POAG is to be able to target effective treatment to individuals who will eventually go blind without it. Epidemiological studies of POAG have not specifically addressed the possibility that nutrition may play a role in the development of POAG. A handful of papers have considered that nutrition may have an impact on POAG patients. POAG is not believed to be a 'vitamin-deficiency disease'. The concept of 'vitamin-deficiency diseases' and the recommended daily allowances have not kept pace with the growing understanding of the cellular and molecular functions of vitamins and other micronutrients. The aetiology of POAG remains a mystery. Discoveries in cell physiology can be assimilated from the literature and applied to known homeostatic mechanisms of the eye. In this way the possible roles of nutritional components involved in the aetiology of POAG can be described. The mechanisms may be subject to many influences in ways that have yet to be defined. Two distinct changes in the trabecular meshwork can be identified: trabecular meshwork changes that cause intra-ocular pressure to increase and trabecular meshwork changes that are directly correlated to optic nerve atrophy. Compelling evidence suggests that collagen trabecular meshwork extracellular matrix (ECM) remodelling is correlated to increased intraocular pressure in POAG. Elastin trabecular meshwork ECM remodelling is correlated to POAG optic nerve atrophy. There appear to be two different pathways of ECM remodelling and apoptosis induction in POAG. The pathway for collagen remodelling and apoptosis induction seems to be exogenously influenced by water-soluble antioxidants, for example, glutathione. The pathway for elastin remodelling and apoptosis induction seems to be influenced by endogenous lipid-soluble antioxidants, for example, vitamin E. Roles can be defined for antioxidants in the two different pathways of ECM remodelling and apoptosis induction. This suggests that antioxidants are important in maintaining cellular homeostasis relevant to the aetiology of POAG.

Alterations in the morphology of lamina cribrosa pores in glaucomatous eyes

AIMS

To determine alterations which occur in the size and shape of lamina cribrosa (LC) pores in glaucomatous eyes over a period of time.

METHODS

Baseline and follow up optic disc photographs were retrospectively studied in 39 eyes of 39 patients with glaucoma. Only eyes with a vertical cup to disc ratio equal to or greater than 0.6 were included in the study. In addition, all selected eyes had to have serial optic disc photographs obtained at least 3 years apart allowing clear visualisation of LC surface. The association of the alterations in LC surface morphology with patient specific and eye specific characteristics was statistically analysed.

RESULTS

During a mean study period of 3.90 (SD 0.7) years, individual pore size (mean pore area to disc area ratio) exhibited a significant decrease between baseline and follow up measurements of each eye (p<0.0001). However, during the study period, total pore area to disc area ratio did not change (p>0.05), and the change in pore shape in some eyes (from circular to more oval and elongated) was statistically insignificant (p = 0.12). Although a relation was detectable between the optic disc and lamina cribrosa parameters at a given time, which reflects cumulative effects, during the study period, there was no significant association between the changes of the LC parameters and neural tissue damage. The rate and the magnitude of the changes in individual pore size during the study period were not significantly different among the eyes exhibiting progressive neural rim damage and those staying stable (p>0.05).

CONCLUSION

These findings demonstrate that the LC surface morphology exhibits changes along with the glaucomatous optic disc damage. However, the clinical appearance of LC surface in glaucomatous eyes may continue to change, even when the neural rim damage is clinically stable. These findings are probably associated with the chronic cellular events of tissue remodelling that occur in the glaucomatous optic nerve head.

Purification of astrocytes from adult human optic nerve heads by immunopanning

Most in vitro studies in the CNS require pure cultures of astrocytes. Astrocytes from the human optic nerve head (ONH, type 1B) represent a specialized population of astrocytes. Primary cells grown from human optic nerve head explants were cultured for 3-4 weeks. To select astrocytes by immunopanning, cell suspensions were placed on a P100 panning dish coated with C5 anti-neuroepithelial antibody and allowed to attach for 30 min. Nonadherent cells were plated on a second dish coated with anti-Thy1.1 antibody to deplete microglia and meningeal cells. Finally, remnant nonadherent cells were plated on a noncoated dish. Purified cells were immunostained with astrocyte markers: GFAP, vimentin, Pax2, A2B5, nestin and NCAM. Other cell types were characterized by HLA-DR for microglia and smooth muscle actin for vascular smooth muscle. The proportion of GFAP+ astrocytes in the cultures was determined by flow cytometry. About 95% of the cells that adhered to the C5 dish were GFAP+ astrocytes. GFAP+ astrocytes expressed vimentin, Pax2, nestin and NCAM, but not A2B5. From the Thy1.1 dish, 60-75% cells were GFAP+ astrocytes and the remainder cells were GFAP- cells. Using cloning rings, we eliminated fibroblast-like cells, smooth muscle and meningeal cells from astrocyte cultures. Smooth muscle cells and fibroblasts grew on the noncoated dish. In conclusion, immunopanning is an efficient method to get high yields of viable type 1B astrocytes from adult human ONH. The current described culture system may provide a valuable tool in studying human optic nerve head biology and disease.

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 NCAM-180 Immunoreactivity and Maintenance of L1 Immunoreactivity in Injured Optic Fibers of Adult Mice

The injury related expression of two axon-growth promoting cell adhesion molecules (CAMs), NCAM-180 which is developmentally downregulated and L1 which is regionally restricted, were compared in optic fibers in the adult mouse. The neuron-specific isoform of NCAM (NCAM-180) is present at very low levels in unlesioned adult optic axons. At 7 days after nerve crush, immunoreactivity was strongly and uniformly increased in optic axons within the nerve and throughout retina. Reactivity in surviving axons had returned to control levels at 4 weeks. To induce regrowth of adult retinal ganglion cell axons retinal explants were placed in culture. Strong NCAM-180 staining was observed on these regenerating optic axons. The neuronal cell adhesion molecule L1 is restricted to retina and to the unmyelinated segment of the optic nerve near the optic nerve head in unlesioned adult animals. Following nerve crush, L1 immunoreactivity was retained within retina and proximal nerve and novel staining was detected in the more distal segment of the optic nerve up to the lesion site where it persisted for at least eight months. The capacity of optic fibers to show increased NCAM-180 immunoreactivity and maintain L1 expression after a lesion may explain why these fibers exhibit relatively good potential for regeneration.

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.

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.

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.