Changes in gene expression in response to mechanical strain in human scleral fibroblasts

Sustained Retinal Defocus Increases the Effect of Induced Myopia on the Retinal Astrocyte Template

The aim of this article is to describe sustained myopic eye growth's effect on astrocyte cellular distribution and its association with inner retinal layer thicknesses. Astrocyte density and distribution, retinal nerve fiber layer (RNFL), ganglion cell layer, and inner plexiform layer (IPL) thicknesses were assessed using immunochemistry and spectral-domain optical coherence tomography on seventeen common marmoset retinas (Callithrix jacchus): six induced with myopia from 2 to 6 months of age (6-month-old myopes), three induced with myopia from 2 to 12 months of age (12-month-old myopes), five age-matched 6-month-old controls, and three age-matched 12-month-old controls. Untreated marmoset eyes grew normally, and both RNFL and IPL thicknesses did not change with age, with astrocyte numbers correlating to RNFL and IPL thicknesses in both control age groups. Myopic marmosets did not follow this trend and, instead, exhibited decreased astrocyte density, increased GFAP+ spatial coverage, and thinner RNFL and IPL, all of which worsened over time. Myopic changes in astrocyte density, GFAP+ spatial coverage and inner retinal layer thicknesses suggest astrocyte template reorganization during myopia development and progression which increased over time. Whether or not these changes are constructive or destructive to the retina still remains to be assessed.

IOP and glaucoma damage: The essential role of optic nerve head and retinal mechanosensors

There are many unanswered questions on the relation of intraocular pressure to glaucoma development and progression. IOP itself cannot be distilled to a single, unifying value, because IOP level varies over time, differs depending on ocular location, and can be affected by method of measurement. Ultimately, IOP level creates mechanical strain that affects axonal function at the optic nerve head which causes local extracellular matrix remodeling and retinal ganglion cell death - hallmarks of glaucoma and the cause of glaucomatous vision loss. Extracellular tissue strain at the ONH and lamina cribrosa is regionally variable and differs in magnitude and location between healthy and glaucomatous eyes. The ultimate targets of IOP-induced tissue strain in glaucoma are retinal ganglion cell axons at the optic nerve head and the cells that support axonal function (astrocytes, the neurovascular unit, microglia, and fibroblasts). These cells sense tissue strain through a series of signals that originate at the cell membrane and alter cytoskeletal organization, migration, differentiation, gene transcription, and proliferation. The proteins that translate mechanical stimuli into molecular signals act as band-pass filters - sensing some stimuli while ignoring others - and cellular responses to stimuli can differ based on cell type and differentiation state. Therefore, to fully understand the IOP signals that are relevant to glaucoma, it is necessary to understand the ultimate cellular targets of IOP-induced mechanical stimuli and their ability to sense, ignore, and translate these signals into cellular actions.

[The value of lamina cribrosa in the diagnosis and treatment of glaucoma. Remodeling of lamina cribrosa collagen and approaches to its therapeutic treatment]

Among the first structures suffering damage with an increase in intraocular pressure (IOP) and in early stage of glaucoma are the lamina cribrosa (LC) and peripapillary sclera (ppScl). Changes in these structures occur at the molecular and cellular level. Extracellular matrix (ECM) is the basis of connective tissue, provides mechanical support for the cells, facilitates intercellular interactions and transport of chemicals, including in LC and ppScl. Mechanical stress causes remodeling and disorganization of the ECM, which leads to changes in the structure of the tissue itself, an increase in its rigidity and a decrease in elasticity. Taking into account the molecular and cellular mechanisms of damage to LC and ppScl, various researchers have developed strategies and tactics for therapeutic intervention on these structures, contributing to a decrease in ECM secretion and, as a consequence, suspension of their remodeling. These approaches may in the future form the basis for the treatment of glaucomatous optic neuropathy.

Effect of TGF-β2 on the Mechanical Properties of Posterior Scleral Fibroblasts in Experimental Myopia

Objective

The effects of TGF-β2 on mechanical properties of sclerotic desmocytes isolated from healthy and myopic guinea pigs were investigated in order to further understand the pathogenesis of myopia. To study the effect of TGF-β2 on the mechanical properties of posterior scleral fibroblasts in experimental myopia.

Methods

A lens-induced myopia (LIM) animal model was developed in 12 guinea pigs, with the opposite eye serving as a self-control (SC). Five untreated guinea pigs served as normal controls. Lenses were removed 30 days after model onset. Primary scleral fibroblasts were isolated and passaged twice and then treated with vehicle control or 1, 10, or 100 ng/mL TGF-β2. After 24 h, micropipette aspiration was used to investigate the viscoelastic properties of the cells.

Results

Scleral fibroblasts from LIM exhibited significantly higher equilibrium moduli and apparent viscosities relative to SC without TGF-β2 treatment. Treatment of LIM or SC scleral fibroblasts with 1 or 10 ng/mL TGF-β2 led to significantly different (p < 0.05) equilibrium moduli and apparent viscosities compared with vehicle control, whereas no significant differences were observed upon treatment with 100 ng/mL TGF-β2. LIM cells treated with 1 and 10 ng/mL TGF-β2 exhibited lower equilibrium moduli and apparent viscosities compared with similarly treated SC cells, but LIM cells and SC cells treated with 100 ng/mL TGF-β2 had similar mechanical properties.

Conclusions

The addition of 1 and 10 ng/mL TGF-β2 can lower the equilibrium modulus and apparent viscosity of scleral fibroblasts in the normal eye.

Remodeling of the Lamina Cribrosa: Mechanisms and Potential Therapeutic Approaches for Glaucoma

Glaucomatous optic neuropathy is the leading cause of irreversible blindness in the world. The chronic disease is characterized by optic nerve degeneration and vision field loss. The reduction of intraocular pressure remains the only proven glaucoma treatment, but it does not prevent further neurodegeneration. There are three major classes of cells in the human optic nerve head (ONH): lamina cribrosa (LC) cells, glial cells, and scleral fibroblasts. These cells provide support for the LC which is essential to maintain healthy retinal ganglion cell (RGC) axons. All these cells demonstrate responses to glaucomatous conditions through extracellular matrix remodeling. Therefore, investigations into alternative therapies that alter the characteristic remodeling response of the ONH to enhance the survival of RGC axons are prevalent. Understanding major remodeling pathways in the ONH may be key to developing targeted therapies that reduce deleterious remodeling.

Inhibition of RhoA/MRTF-A signaling alleviates nucleus pulposus fibrosis induced by mechanical stress overload

PURPOSE/AIM

: Intervertebral disc degeneration (IDD) is the leading cause of lower back pain, and clinically useful drugs for IDD are unavailable. Mechanical stress overload-induced fibrosis plays a critical role in IDD. RhoA/MRTF-A signaling is known to regulate tissue fibrosis; however, the effect of RhoA/MRTF-A on the development of IDD is unclear.

MATERIALS AND METHODS

: The expression of aggrecan, collagen I, collagen II, MMP-12, CTGF, and MRTF-A in nucleus pulposus (NP) samples from IDD patients and controls was detected by immunohistochemical staining. Primary nucleus pulposus cells (NPCs) were isolated and cultured to establish an overload strain model treated with or without CCG-1423. The protein levels of RhoA, ROCK2, MRTF-A, CTGF, and MMP-12 as well as fibrosis-associated proteins were detected by western blotting and immunofluorescence.

RESULTS

: Collagen I, MMP-12, and CTGF were significantly upregulated, and aggrecan and collagen II were significantly downregulated in the IDD samples. The cellular localization of MRTF-A was associated with intervertebral disc (IVD) degeneration. Overloaded strain enhanced the nuclear translocation of MRTF-A and changed the NPC morphology from spindle-shaped to long strips. Additional experiments showed that RhoA, ROCK2, MRTF-A, SRF, MMP-12, and CTGF were upregulated; however, aggrecan and collagen II were downregulated in NPCs under overload strain. CCG-1423, a RhoA/MRTF-A pathway inhibitor, reversed strain-induced fibrosis.

CONCLUSION

: Mechanical stress activates RhoA/MRTF-A signaling to promote extracellular matrix (ECM) degeneration in the NP, which is associated with the development of IDD. Our findings suggest that the RhoA/MRTF-A inhibitor CCG-1423 can alleviate NPC degeneration caused by overload stress and has potential as a therapeutic agent for IDD.

Study of the effects of rabbit scleral fibroblasts on cellular biomechanical properties and MMP-2 expression using two modes of riboflavin/ultraviolet A wave collagen cross-linking

OBJECTIVE

The aim of this study is to evaluate the cellular biomechanical properties and MMP-2 expression changes in rabbit scleral fibroblasts using two modes of riboflavin and ultraviolet A (UVA) collagen cross-linking (CXL).

METHODS

Twenty-four New Zealand white rabbits were randomly divided into two groups, A and B. The left eye was chosen for the experimental group and the right eye for the control group. In group A, the eyes were irradiated for 30 min, with a power density of 3.0 mW/cm². In group B, the eyes were irradiated for 9 min, with a power density of 10.0 mW/cm². One week after CXL, full-field electroretinography was performed. Sixty days after CXL, the rabbits were sacrificed, and scleral fibroblasts were extracted from the CXL-treated sclera area and corresponding parts of control sclera and cultured. Cellular biomechanical properties were evaluated using the micropipette aspiration technique, and the MMP-2 protein expression was determined by Western blot analysis.

RESULTS

There was no statistical difference in the amplitude and latency of the dark adaptation 3.0 and light adaptation 3.0 between the CXL and control eyes of groups A and B (P > 0.05). Compared with the control groups, the Young's modulus of the fibroblasts and apparent viscosity of the experimental eyes in groups A and B were increased after CXL (P < 0.05), but there was no significant difference between the two groups under different irradiation modes (P > 0.05). The MMP-2 expression in scleral fibroblasts from experimental eyes was significantly higher than that in scleral fibroblasts from control eyes in groups A and B. Under the two different irradiation modes, the MMP-2 expression in the scleral fibroblasts from experimental eyes in group A was significantly higher than that in the scleral fibroblasts from experimental eyes in group B.

CONCLUSION

The riboflavin-UVA scleral CXL conducted in two different modes produced no significant side effects on the retina and could strengthen the cell biomechanical properties as well as increase the MMP-2 expression of scleral fibroblasts significantly.

Identification of key genes and pathways in scleral extracellular matrix remodeling in glaucoma: Potential therapeutic agents discovered using bioinformatics analysis

Background: Glaucoma is a leading cause of irreversible blindness. Remodeling of the scleral extracellular matrix (ECM) plays an important role in the development of glaucoma. The aim of this study was to identify the key genes and pathways for the ECM remodeling of sclera in glaucoma by bioinformatics analysis and to explore potential therapeutic agents for glaucoma management. Methods: Genes associated with glaucoma, sclera and ECM remodeling were detected using the text mining tool pubmed2ensembl, and assigned Gene Ontology (GO) biological process terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways using the GeneCodis program. A protein-protein interaction (PPI) network was constructed by STRING and visualized in Cytoscape, module analysis was performed using the Molecular Complex Detection (MCODE) plugin, and GO and KEGG analyses of the gene modules were performed using the Database of Annotation, Visualization and Integrated Discovery (DAVID) platform. The genes that clustered in the significant module were selected as core genes, and functions and pathways of the core genes were visualized using ClueGO and CluePedia. Lastly, the drug-gene interaction database was used to explore drug-gene interactions of the core genes to find drug candidates for glaucoma. Results: We identified 125 genes common to "Glaucoma", "Sclera", and "ECM remodeling" by text mining. Gene functional enrichment analysis yielded 30 enriched GO terms and 20 associated KEGG pathways. A PPI network that included 60 nodes with 249 edges was constructed, and three gene modules were obtained using the MCODE. We selected 13 genes that clustered in module 1 as core candidate genes that were associated mainly with ECM degradation and cell proliferation and division. The HIF-1 signaling pathway, FOXO signaling pathway, PI3K-Akt signaling pathway and TGFB signaling pathway were found to be enriched. We found that 11 of the 13 selected genes could be targeted by 26 existing drugs. Conclusions: The results showed that VEGFA, TGFB1, TGFB2, TGFB3, IGF2, IGF1, EGF, FN1, KNG1, TIMP1, SERPINE1, THBS1, and VWF were potential key genes involved to scleral ECM remodeling. Furthermore, 26 drugs were identified as potential therapeutic agents for glaucoma treatment and management.

The Dynamic Scleral Extracellular Matrix Alterations in Chronic Ocular Hypertension Model of Rats

Intraocular pressure (IOP) generates stress and strains in the laminar cribrosa and sclera, which may affect the development and progression of glaucoma. Scleral stiffness and material components have changed under elevated IOP. However, the detailed changes of the components of the hypertensive sclera are not well understood. In this study, we aimed to investigate the changes of the main components in the scleral extracellular matrix (ECM), and matrix metalloproteinase 2 (MMP2) and their relationship with time under chronic elevated IOP in Sprague–Dawley rats. An ocular hypertension model was established in the right eyes by anterior chamber injection with 0.3% carbomer solution. The left eye was used as the contralateral control. Immunofluorescent imaging of the tissue frozen sections, Western blot analysis, and quantitative PCR (qPCR) were performed to detect the expressions of type I collagen (COL1), elastin, and MMP2 in the sclera. The ocular hypertension model was successfully established. As compared to the left eyes, the immunofluorescence imaging, Western blot analysis, and qPCR showed that COL1, elastin, and MMP2 were significantly increased in the right eyes at 1 week (all P < 0.05). At 2 weeks, COL1 in the right eyes tended to be lower than that in the left eyes, while elastin and MMP2 were still higher (all P < 0.05) in the right eyes. When the IOP was elevated for 4 weeks, both COL1 and MMP2 were lower than those in the left eyes (all P < 0.05), while elastin between the two eyes was similar (P > 0.05). Under this 4-week hypertensive state, COL1 and elastin were initially elevated at 1 week, and then obviously reduced from 2 to 4 weeks. Consistently, MMP2 was gradually increased, with a peak at 2 weeks, and then decreased at 4 weeks. In conclusion, the chronic elevated IOP induced dynamic scleral ECM alterations in rats in a pressure- and time-dependent manner. MMP2 may play an important role in the balance between ECM synthesis and degradation and could potentially be a novel target for glaucoma intervention.

Mechanical strain affects collagen metabolism-related gene expression in scleral fibroblasts

We previously demonstrated that collagen metabolism affects scleral mechanical properties and scleral remodeling. Scleral remodeling changes the mechanical strain on sclera and scleral fibroblasts. We postulated that mechanical strain changes affect collagen metabolism in scleral fibroblasts. To understand the differences in collagen metabolism in scleral fibroblasts related to mechanical strain changes, scleral fibroblasts were isolated and cultured under different mechanical strains using the FX-4000 system or were treated with the TGF-β1 and TGFBR1 inhibitor LY364947. The collagen metabolism-related gene expression levels were detected. The results showed that the appropriate (lower) mechanical strain improved collagen synthesis and reduced collagen decomposition. In contrast, higher mechanical strain reduced collagen synthesis and enhanced collagen decomposition, especially a sustained higher strain. Furthermore, the effect of a transitory higher strain was recoverable, and collagen metabolism in scleral fibroblasts was regulated by TGF-β1. These results suggested that mechanical strain mediates TGF-β1 expression to regulate collagen metabolism in scleral fibroblasts, thereby affect scleral tissue remodeling.

Scleral structure and biomechanics

As the eye's main load-bearing connective tissue, the sclera is centrally important to vision. In addition to cooperatively maintaining refractive status with the cornea, the sclera must also provide stable mechanical support to vulnerable internal ocular structures such as the retina and optic nerve head. Moreover, it must achieve this under complex, dynamic loading conditions imposed by eye movements and fluid pressures. Recent years have seen significant advances in our knowledge of scleral biomechanics, its modulation with ageing and disease, and their relationship to the hierarchical structure of the collagen-rich scleral extracellular matrix (ECM) and its resident cells. This review focuses on notable recent structural and biomechanical studies, setting their findings in the context of the wider scleral literature. It reviews recent progress in the development of scattering and bioimaging methods to resolve scleral ECM structure at multiple scales. In vivo and ex vivo experimental methods to characterise scleral biomechanics are explored, along with computational techniques that combine structural and biomechanical data to simulate ocular behaviour and extract tissue material properties. Studies into alterations of scleral structure and biomechanics in myopia and glaucoma are presented, and their results reconciled with associated findings on changes in the ageing eye. Finally, new developments in scleral surgery and emerging minimally invasive therapies are highlighted that could offer new hope in the fight against escalating scleral-related vision disorder worldwide.

Deep Optic Nerve Head Morphology Is Associated With Pattern of Glaucomatous Visual Field Defect in Open-Angle Glaucoma

Purpose

We investigated the relationship between visual field (VF) defect pattern and deep optic nerve head (ONH) morphology in open angle glaucoma (OAG) eyes using spectral-domain optical coherence tomography (SD-OCT).

Methods

Of 278 OAG eyes, 169 with and 55 without externally oblique border tissue (EOBT) were included in the final analysis. Enhance depth imaging SD-OCT was used to measure the deep ONH parameters, such as EOBT length, ONH tilt angle, and optic canal (OC) obliqueness. The extents and locations of the maximum deep ONH parameters were explored according to VF pattern in OAG eyes.

Results

OAG eyes with EOBT showed longer axial length (AL; 25.6 vs. 24.4 mm; P < 0.001) and greater superior VF defects (67.5% vs. 49.1%; P = 0.02) compared to OAG eyes without EOBT. Multivariate logistic regression analysis revealed that relatively inferior location of maximum deep ONH parameters was associated with superior hemifield defects dominant in OAG (P < 0.001 in all parameters). In addition, the locations of maximum deep ONH parameters were consistent with dominant VF defect locations in OAG eyes with AL < 24.5 mm. The presence of paracentral scotoma in OAG was associated with worse mean deviation (MD) and relatively inferior location of deep ONH parameters.

Conclusions

The locations of maximum deep ONH parameters were associated with the location of dominant VF defects and presence of paracentral scotoma in OAG eyes.

Differential gene expression of BMP2 and BMP receptors in chick retina & choroid induced by imposed optical defocus

Recent studies have demonstrated the defocus sign-dependent, bidirectional gene expression regulation of bone morphogenetic proteins, BMP2, 4 and 7 in chick RPE. In this study, we examined the effects of imposed positive (+10 D) and negative (-10 D) lenses on the gene expression of these BMPs and BMP receptors (BMPR1A, BMPR1B, BMPR2) in chick retina and choroid after monocular lens treatment for 2 or 48 h, as indicators of the roles of retinal and choroidal BMPs and receptors in postnatal eye growth regulation. In retina, although all genes were expressed, neither +10 nor -10 D lenses, worn for either 2 or 48 h, significantly altered gene expression. In contrast, treatment-related differential gene expression was detected in the choroid for both BMPs and their receptors, although interestingly, with the +10 D lens, BMP2 was up-regulated by 156.7 ± 19.7% after 2 h, while BMPR1A was down-regulated to 82.3 ± 12.5% only after 48 h. With the -10 D lens, only the gene expression of BMPR1B was significantly altered, being up-regulated by 162.3 ± 21.2% after 48 h. Untreated birds showed no difference in expression between their two eyes, for any of the genes examined. The finding that retinal gene expression for BMP2, 4, 7 and their receptors are not affected by short-term optical defocus contrasts with previous observations of sign-dependent expression changes for the same genes in the RPE. The latter changes were also larger and more consistent in direction than the choroidal gene expression changes reported here. The interrelationship between these various changes and their biological significance for eye growth regulation are yet to be elucidated.

A Bioengineering Approach to Myopia Control Tested in a Guinea Pig Model

Purpose

To investigate the biocompatibility of an injectable hydrogel and its ability to control myopia progression in guinea pigs.

Methods

The study used a hydrogel synthesized from acrylated hyaluronic acid with a conjugated cell-binding peptide and enzymatically degradable crosslinker. Seven-day-old guinea pigs were first form deprived (FD) with diffusers for 1 week. One group was kept as an FD-only control; two groups received a sub-Tenon's capsule injection of either hydrogel or buffer (sham surgery) at the posterior pole of the eye. Form deprivation treatments were then continued for 3 additional weeks. Treatment effects were evaluated in terms of ocular axial length and refractive error. Safety was evaluated via intraocular pressure (IOP), visual acuity, flash electroretinograms (ERG), and histology.

Results

Both hydrogel and sham surgery groups showed significantly reduced axial elongation and myopia progression compared to the FD-only group. For axial lengths, net changes in interocular difference (treated minus control) were 0.04 ± 0.06, 0.02 ± 0.09, and 0.24 ± 0.08 mm for hydrogel, sham, and FD-only groups, respectively (P = 0.0006). Intraocular pressures, visual acuities, and ERGs of treated eyes were not significantly different from contralateral controls. Extensive cell migration into the implants was evident. Both surgery groups showed noticeable Tenon's capsule thickening.

Conclusions

Sub-Tenon's capsule injections of both hydrogel and buffer inhibited myopia progression, with no adverse effects on ocular health. The latter unexpected effect warrants further investigation as a potential novel myopia control therapy. That the hydrogel implant supported significant cell infiltration offers further proof of its biocompatibility, with potential application as a tool for drug and cell delivery.

Adult human dermal fibroblasts exposed to nanosecond electrical pulses exhibit genetic biomarkers of mechanical stress

Background

Exposure of cells to very short (<1 µs) electric pulses in the megavolt/meter range have been shown to cause a multitude of effects, both physical and molecular in nature. Physically, nanosecond electrical pulses (nsEP) can cause disruption of the plasma membrane, cellular swelling, shrinking and blebbing. Molecularly, nsEP have been shown to activate signaling pathways, produce oxidative stress, stimulate hormone secretion and induce both apoptotic and necrotic death. We hypothesize that studying the genetic response of primary human dermal fibroblasts exposed to nsEP, will gain insight into the molecular mechanism(s) either activated directly by nsEP, or indirectly through electrophysiology interactions.

Methods

Microarray analysis in conjunction with quantitative real time polymerase chain reaction (qRT-PCR) was used to screen and validate genes selectively upregulated in response to nsEP exposure.

Results

Expression profiles of 486 genes were found to be significantly changed by nsEP exposure. 50% of the top 20 responding genes coded for proteins located in two distinct cellular locations, the plasma membrane and the nucleus. Further analysis of five of the top 20 upregulated genes indicated that the HDFa cells’ response to nsEP exposure included many elements of a mechanical stress response.

Conclusions

We found that several genes, some of which are mechanosensitive, were selectively upregulated due to nsEP exposure. This genetic response appears to be a primary response to the stimuli and not a secondary response to cellular swelling.

General significance

This work provides strong evidence that cells exposed to nsEP interpret the insult as a mechanical stress.

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Global gene expression analysis was performed on primary cells exposed to nsEP.

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The bioeffects of nsEP on adult human dermal fibroblasts were investigated.

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Microarray analysis suggests nsEP imparts a mechanical stress on cells.

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FOS, NR4A2, ITPKB, KLHL24, and SOD2 were upregulated in response to nsEP.

Combined effects of interleukin-1β and cyclic stretching on metalloproteinase expression in corneal fibroblasts in vitro

Background

Corneal tensile strain increases if the cornea becomes thin or if intraocular pressure increases. However, the effects of mechanical stress on extracellular matrix (ECM) remodelling in the corneal repair process and the corneal anomalies are unknown.

Methods

In this study, the combined effects of interleukin-1β (IL-1β) on matrix metalloproteinases (MMPs) in corneal fibroblasts under cyclic stretching were investigated in vitro. Cultured rabbit corneal fibroblasts were subjected to 5, 10 or 15 % cyclic equibiaxial stretching at 0.1 Hz for 36 h in the presence of IL-1β. Conditioned medium was harvested for the analysis of MMP2 and MMP9 protein production using the gelatin zymography and western blot techniques.

Results and conclusions

Cyclic equibiaxial stretching changed the cell morphology by increasing the contractility of F-actin fibres. IL-1β alone induced the expression of MMP9 and increased the production of MMP2, and 5 % stretching alone decreased the production of MMP2, which indicates that a low stretching magnitude can reduce ECM degradation. In the presence of IL-1β, 5 and 10 % stretching increased the production of MMP2, whereas 15 % stretching increased the production of MMP9. These results indicate that MMP expression is enhanced by cyclic mechanical stimulation in the presence of IL-1β, which is expected to contribute to corneal ECM degradation, leading to the development of post-refractive surgery keratectasia.

Evaluation of the Genetic Response of U937 and Jurkat Cells to 10-Nanosecond Electrical Pulses (nsEP)

Nanosecond electrical pulse (nsEP) exposure activates signaling pathways, produces oxidative stress, stimulates hormone secretion, causes cell swelling and induces apoptotic and necrotic death. The underlying biophysical connection(s) between these diverse cellular reactions and nsEP has yet to be elucidated. Using global genetic analysis, we evaluated how two commonly studied cell types, U937 and Jurkat, respond to nsEP exposure. We hypothesized that by studying the genetic response of the cells following exposure, we would gain direct insight into the stresses experienced by the cell and in turn better understand the biophysical interaction taking place during the exposure. Using Ingenuity Systems software, we found genes associated with cell growth, movement and development to be significantly up-regulated in both cell types 4 h post exposure to nsEP. In agreement with our hypothesis, we also found that both cell lines exhibit significant biological changes consistent with mechanical stress induction. These results advance nsEP research by providing strong evidence that the interaction of nsEPs with cells involves mechanical stress.

Histologic differences between primary high myopia and secondary high myopia due to congenital glaucoma

PURPOSE

To search for histomorphometric differences between eyes with primary high myopia (PHM) or secondary high axial myopia (SHM) caused by congenital glaucoma, and non-highly myopic eyes (NHM).

METHODS

Histologic anterior-posterior sections were histomorphometrically examined.

RESULTS

The investigation included 58 human globes (mean age: 61.5 ± 18.5 years; axial length: 27.3 ± 4.0 mm; range: 21.0-39.0 mm). Bruch's membrane thickness was thinner in SHM than in PHM (posterior pole: p = 0.007; parapapillary region: p = 0.007); midpoint posterior pole/equator = 0.05) and thinner in SHM than in NHM (all p < 0.04), while PHM and NHM did not differ (all p > 0.50). Choroidal thickness did not differ (all p ≥ 0.40) at any measurement location between SHM and PHM, and was thinner (p < 0.05) in both myopic groups than in NHM. Posterior sclera was thinner (p < 0.001) in both myopic groups than in NHM, with no significant difference between both myopic groups. Pars plana scleral thickness was thinner (p = 0.02) in SHM than in PHM after adjusting for axial length. Scleral volume (p = 0.41) and choroidal volume (p = 0.74) did not differ between any of the groups.

CONCLUSIONS

Thinning of Bruch's membrane overall is typical for SHM while eyes with PHM have a normal Bruch's membrane thickness. It may point to Bruch's membrane as an active part in the process of emmetropization/myopization. SHM in contrast to PHM showed scleral thinning in the pars plana region suggesting that the process of emmetropization/myopization takes place posterior to the pars plana. Both SHM and PHM unspecifically showed an axial length associated with thinning of choroid and posterior sclera, while both myopic groups did not differ with NHM in choroidal and scleral volume.

Scleral Mechanisms Underlying Ocular Growth and Myopia

In the regulation of ocular growth, scleral events critically determine eye size and thus the refractive status of the eye. Increased scleral matrix remodeling can lead to exaggerated eye growth causing myopia and additionally increased risk of ocular pathological complications. Thus, therapies targeting these changes in sclera hold potential to limit such complications since sclera represents a relatively safe and accessible drug target. Understanding the scleral molecular mechanisms underlying ocular growth is essential to identifying plausible therapeutic targets in the sclera. This section provides a brief update on molecular studies that pertain to the sclera in the context of ocular growth regulation and myopia.

The Thrombospondin1-TGF-β Pathway and Glaucoma

Glaucoma is characterized by abnormal remodeling of the extracellular matrix (ECM) in the trabecular meshwork and in the connective tissue beams of the lamina cribrosa (LC) at the optic nerve head (ONH), which is associated with axonal damage. Mechanical strain can stimulate ECM remodeling and increased expression of matricellular proteins. Thrombospondins 1 and 2 are induced by cyclic mechanical strain in the eye in both the trabecular meshwork and in the LC region of the ONH. TGF-betas 1 and 2 are increased in glaucoma and play a role in the pathologic remodeling of the ECM in the eye in glaucoma. In this study, we address the role of thrombospondin1 as a regulator of latent TGF-beta activation and discuss the potential therapeutic use of antagonists of the thrombospondin1-TGF-beta pathway for treatment of glaucoma.

Form-deprivation myopia induces decreased expression of bone morphogenetic protein-2, 5 in guinea pig sclera

AIM

To identify the presence of various bone morphogenetic proteins (BMPs) and their receptors in normal sclera of human, rat and guinea pigs, and to determine whether their expression changed with form-deprivation myopia (FDM) in guinea pig sclera.

METHODS

The expression of BMPs and BMP receptors were detected using reverse transcription polymerase chain reaction (RT-PCR) and immunofluorescence. Two-week-old guinea pigs were monocularly form-deprived with a translucent lens. After fourteen days induction of FDM, total RNA was isolated and subjected to RT-PCR to examine the changes of BMPs and BMP receptors in tissues from the posterior sclera. Western blotting analysis was used to investigate their changes in protein levels.

RESULTS

Human sclera expressed mRNAs for BMP-2, -4, -5, -7, -RIA, -RIB and BMP-RII. Conversely, rat sclera only expressed mRNA for BMP-7 and BMP-RIB, while the expression of BMPs and BMP receptors in guinea pigs were similar to that of humans. Human sclera also expresses BMP-2, -4, -5,-7 in protein level. Fourteen days after the induction of myopia, significant decreased expressions for BMP-2 and BMP-5 in the posterior sclera of FDM-affected eyes (P<0.05 vs internal control eyes).

CONCLUSION

Various BMPs were expressed in human and guinea pig sclera. In the posterior sclera, expressions of BMP-2 and BMP-5 significantly decreased in FDM eyes. This finding indicates that various BMPs as components of the scleral cytokines regulating tissue homeostasis and provide evidence that alterations in the expression of BMP-2 and BMP-5 are associated with sclera remodeling during myopia induction.

Changes in scleral collagen organization in murine chronic experimental glaucoma

PURPOSE

The organization of scleral collagen helps to determine the eye's biomechanical response to intraocular pressure (IOP), and may therefore be important in glaucoma. This study provides a quantitative assessment of changes in scleral collagen fibril organization in bead-induced murine experimental glaucoma.

METHODS

Wide-angle X-ray scattering was used to study the effect of bead-induced glaucoma on posterior scleral collagen organization in one eye of 12 CD1 mice, with untreated fellow eyes serving as controls. Three collagen parameters were measured: the local preferred fibril directions, the degree of collagen anisotropy, and the total fibrillar collagen content.

RESULTS

The mouse sclera featured a largely circumferential orientation of fibrillar collagen with respect to the optic nerve head canal. Localized alteration to fibril orientations was evident in the inferior peripapillary sclera of bead-treated eyes. Collagen anisotropy was significantly (P<0.05) reduced in bead-treated eyes in the superior peripapillary (Treated: 43±8%;

CONTROL

49±6%) and midposterior (Treated: 39±4%;

CONTROL

43±4%) sclera, and in the peripapillary region overall (Treated: 43±6%;

CONTROL

47±3%). No significant differences in total collagen content were found between groups.

CONCLUSIONS

Spatial changes in collagen fibril anisotropy occur in the posterior sclera of mice with bead-induced chronic IOP elevation and axonal damage. These results support the idea that dynamic changes in scleral form and structure play a role in the development of experimental glaucoma in mice, and potentially in human glaucoma.

Expression of MMP-2, MT1-MMP, and TIMP-2 by cultured rabbit corneal fibroblasts under mechanical stretch

Refractive surgery not only leads to tissue injury but also evokes mechanical stress increase of the cornea. How the mechanical stress affects the corneal matrix remodeling, specifically, matrix metalloproteinases (MMPs) and their inhibitors (tissue inhibitors of metalloproteinases; TIMPs) is not well understood. In this study, cultured rabbit corneal fibroblasts in vitro were subjected to regimen of 5%, 10%, or 15% equibiaxial stretch at 0.1 Hz for 3 or 24 h. MMP-2 protein level was measured by gelatin zymography and Western blotting. MMP-2, membrane type 1 MMP (MT1-MMP), and TIMP-2 mRNA levels were quantified by real-time quantitative PCR. Extracellular regulated protein kinase (ERK) phosphorylation protein levels were assessed by Western blotting. Our results showed that a 15% stretch resulted in increases in MMP-2 protein, MMP-2 mRNA, and MT1-MMP mRNA levels, but a decrease in TIMP-2 mRNA level. However, a 5% stretch caused decreases in MMP-2 protein and mRNA level, but an increase in TIMP-2 mRNA level, and no change in MT1-MMP mRNA level. A 15% stretch also caused a significant increase in ERK1/2 phosphorylation. Inhibition of the mitogenactivated protein kinase (MEK) pathway with PD98059 attenuated stretch-induced increase in MMP-2 production and ERK activity. These results suggest that small-magnitude stretching may promote corneal matrix synthetic events, whereas large-magnitude stretching promotes corneal matrix degradation by changing the balance between MMPs and TIMPs in corneal fibroblasts. Large-magnitude stretch-induced increase in pro-MMP-2 production was in an ERK-dependent manner.

Scleral cross section area and volume and axial length

Purpose

To examine whether the scleral cross sectional area and estimated scleral volume are associated with a longer axial length in human eyes.

Methods

Histologic anterior-posterior sections running through the pupil and the optic nerve head were examined. Using a light microscope, we measured the thickness of the sclera at the limbus, ora serrata, equator, midpoint between equator and posterior pole (MPEPP), peripapillary region and posterior pole. Additionally we determined the length and the cross section area of the sclera.

Results

The histomorphometric study included 214 human globes of 214 subjects (mean age: 62.5±13.9 years) (147 eyes enucleated due to malignant choroidal melanoma or due to other non-glaucomatous reasons; 67 eyes enucleated due to secondary angle-closure glaucoma). Mean axial length was 25.1±1.8 mm (median: 24.0 mm; range: 20–35 mm). Scleral thickness measurements decreased with increasing axial length for values taken at the equator (P = 0.008; correlation coefficient r = −0.18), MPEPP (P<0.001;r:−0.47), optic nerve head border (P<0.001;r = −0.47) and posterior pole (P<0.001;r = −0.54). Scleral cross section area decreased significantly with increasing axial lengths for the regions at or behind the equator (P = 0.002;r = −0.21), at or behind the MPEPP (P = 0.001;r = −0.25), and at or behind the optic nerve head border (P = 0.001;r = −0.24). Scleral volume measurements were not significantly associated with axial length

Conclusions

Despite an associated increase in surface area, eyes with longer axial length do not have an increase in scleral volume. It may point against a scleral volume enlargement to play a role in the process of axial elongation.

Biomechanics of the Posterior Eye: A Critical Role in Health and Disease

The posterior eye is a complex biomechanical structure. Delicate neural and vascular tissues of the retina, choroid, and optic nerve head that are critical for visual function are subjected to mechanical loading from intraocular pressure, intraocular and extraorbital muscles, and external forces on the eye. The surrounding sclera serves to counteract excessive deformation from these forces and thus to create a stable biomechanical environment for the ocular tissues. Additionally, the eye is a dynamic structure with connective tissue remodeling occurring as a result of aging and pathologies such as glaucoma and myopia. The material properties of these tissues and the distribution of stresses and strains in the posterior eye is an area of active research, relying on a combination of computational modeling, imaging, and biomechanical measurement approaches. Investigators are recognizing the increasing importance of the role of the collagen microstructure in these material properties and are undertaking microstructural measurements to drive microstructurally-informed models of ocular biomechanics. Here, we review notable findings and the consensus understanding on the biomechanics and microstructure of the posterior eye. Results from computational and numerical modeling studies and mechanical testing of ocular tissue are discussed. We conclude with some speculation as to future trends in this field.

Gene expression signatures in tree shrew sclera in response to three myopiagenic conditions

PURPOSE

We compared gene expression signatures in tree shrew sclera produced by three different visual conditions that all produce ocular elongation and myopia: minus-lens wear, form deprivation, and dark treatment.

METHODS

Six groups of tree shrews (n = 7 per group) were used. Starting 24 days after normal eye-opening (days of visual experience [DVE]), two minus-lens groups wore a monocular -5 diopter (D) lens for 2 days (ML-2) or 4 days (ML-4); two form-deprivation groups wore a monocular translucent diffuser for 2 days (FD-2) or 4 days (FD-4). A dark-treatment (DK) group was placed in continuous darkness for 11 days after experiencing a light/dark environment until 17 DVE. A normal colony-reared group was examined at 28 DVE. Quantitative PCR was used to measure the relative differences in mRNA levels for 55 candidate genes in the sclera that were selected, either because they showed differential expression changes in previous ML studies or because a whole-transcriptome analysis suggested they would change during myopia development.

RESULTS

The treated eyes in all groups responded with a significant myopic shift, indicating that the myopia was actively progressing. In the ML-2 group, 27 genes were significantly downregulated in the treated eyes, relative to control eyes. In the treated eyes of the FD-2 group, 16 of the same genes also were significantly downregulated and one was upregulated. The two gene expression patterns were significantly correlated (r(2) = 0.90, P < 0.001). After 4 days of treatment, 31 genes were significantly downregulated in the treated eyes of the ML-4 group and three were upregulated. Twenty-nine of the same genes (26 down- and 3 up-regulated) and six additional genes (all downregulated) were significantly affected in the FD-4 group. The response patterns were highly correlated (r(2) = 0.95, P < 0.001). When the DK group (mean of right and left eyes) was compared to the control eyes of the ML-4 group, the direction and magnitude of the gene expression patterns were similar to those of the ML-4 (r(2) = 0.82, P < 0.001, excluding PENK). Similar patterns also were found when the treated eyes of the ML-4, FD-4, and DK groups were compared to the age-matched normal eyes.

CONCLUSIONS

The very similar gene expression signatures produced in the sclera by the three different myopiagenic visual conditions at different time points suggests that there is a "scleral remodeling signature" in this mammal, closely related to primates. The scleral genes examined did not distinguish between the specific visual stimuli that initiate the signaling cascade that results in axial elongation and myopia.

Mechanical stretching induces matrix metalloproteinase-2 expression in rat retinal glial (Müller) cells

Pathological myopia, as one of the leading causes of blindness, is characterized by excessive and progressive elongation of the eyeball with concomitant degenerative changes in the posterior segment of the eye. During the progressive distension of the posterior pole, the retina, choroid, and sclera are subjected to constant mechanical force, as a result of which, tissue remodeling occurs. Active remodeling of the sclera in myopia has been studied intensively. By comparison, retinal remodeling under mechanical stretching has attracted little attention, and further research is therefore required. In this study, we showed that constant mechanical stretching of rat retinal Müller cells for 24 h led to a significant increase in the intracellular matrix metalloproteinase-2 mRNA and protein levels. The extracellular secretory matrix metalloproteinase-2 protein levels and activity were also enhanced. These results suggest a possible novel molecular mechanism that would account for retinal remodeling in many ocular diseases in which the retina is often overstretched, such as pathological myopia and proliferative vitreoretinopathy.

Gene expression changes under cyclic mechanical stretching in rat retinal glial (Müller) cells

Objective

The retina is subjected to tractional forces in various conditions. As the predominant glial element in the retina, Müller cells are active players in all forms of retinal injury and disease. In this study, we aim to identify patterns of gene expression changes induced by cyclic mechanical stretching in Müller cells.

Methods

Rat Müller cells were seeded onto flexible bottom culture plates and subjected to a cyclic stretching regimen of 15% equibiaxial stretching for 1 and 24 h. RNA was extracted and amplified, labeled, and hybridized to rat genome microarrays. The expression profiles were analyzed using GeneSpring software, and gene ontology analysis and the Kyoto Encyclopedia of Genes and Genomes (KEGG) were used to select, annotate, and visualize genes by function and pathway. The selected genes of interest were further validated by Quantitative Real-time PCR (qPCR).

Results

Microarray data analysis showed that at 1 and 24 h, the expression of 532 and 991 genes in the Müller cells significantly (t-test, p<0.05) differed between the mechanically stretched and unstretched groups. Of these genes, 56 genes at 1 h and 62 genes at 24 h showed more than a twofold change in expression. Several genes related to response to stimulus (e.g., Egr2, IL6), cell proliferation (e.g., Areg, Atf3), tissue remodeling (e.g., PVR, Loxl2), and vasculogenesis (e.g., Epha2, Nrn1) were selected and validated by qPCR. KEGG pathway analysis showed significant changes in MAPK signaling at both time points.

Conclusions

Cyclic mechanical strain induces extensive changes in the gene expression in Müller cells through multiple molecular pathways. These results indicate the complex mechanoresponsive nature of Müller cells, and they provide novel insights into possible molecular mechanisms that would account for many retinal diseases in which the retina is often subjected to mechanical forces, such as pathological myopia and proliferative vitreoretinopathy.

Effects of imposed defocus of opposite sign on temporal gene expression patterns of BMP4 and BMP7 in chick RPE

This study investigated the effects of imposed optical defocus on the expression patterns of bone morphogenetic protein 4 and 7 (BMP4, BMP7) in chick retinal pigment epithelium (RPE), as indicators of roles in postnatal eye growth regulation. BMP4 and BMP7 gene and protein expression patterns were characterized for retina, RPE and choroid tissues of young normal White-Leghorn chickens. The effects of short-term (2 and 48 h) exposure to monocular +10 and -10 diopter (D) lenses on RPE gene expression of BMP4 and BMP7 were also examined. Tissues from both treated and fellow eyes as well as from eyes of age-matched untreated birds were included in the latter experiment. Of ocular tissues comprising the posterior wall of the chick eye, RPE showed the highest expression of BMP4 and BMP7 mRNA, compared to retina and choroid. Western blots and immunohistochemistry confirmed the expression of BMP4 and BMP7 protein in all layers - retina, RPE, choroid and sclera. With imposed defocus, both BMP4 and BMP7 showed bidirectional changes in expression in RPE, however, with different temporal patterns. With +10 D lenses, BMP4 gene expression was up-regulated after both 2 and 48 h of treatment, while BMP7 expression was up-regulated only after 48 h of lens wear. With -10 D lenses, both BMP4 and BMP7 showed down-regulation of gene expression for both 2 and 48 h treatment durations. With the -10 D lens treatment applied for 48 h, gene expression for both BMP4 and BMP7 was also down-regulated in contralateral fellows of treated eyes compared to eyes of untreated chicks. The rapid changes in gene expression in chick RPE observed for both BMP4 and BMP7, up or down according to the sign of imposed optical defocus, resemble similar trends reported for BMP2. Further studies are needed to confirm the roles of BMPs as ocular growth modulators, as suggested by these data. The data also suggest a role for the RPE as a conduit for relaying growth modulatory retinal signals.

Distribution of bone morphogenetic protein receptors in human scleral fibroblasts cultured in vitro and human sclera

AIM

To investigate the distribution of bone morphogenetic protein receptors (BMPRs) in human scleral fibroblsasts (HSFs) and in human sclera.

METHODS

Primary HSFs were cultured in vitro. The mRNA levels of BMP-2 and BMPRs in HSFs were assayed by reverse transcription-polymerase chain reaction (RT-PCR). The protein distributions of BMP-2 and BMPRs in HSFs were further detected by immunocytofluorescence and western blot. Their protein expression was also detected in frozen human posterior scleral sections by immunohistofluorescence.

RESULTS

BMP-2 and BMPRs were expressed in both HSFs and human sclera not only at mRNA level but also at protein level. The expressions of BMPRIA and BMPRII were higher than that of BMPRIB in the cytoplasm and cell membrane of HSFs in vitro. Western blot further verified the results of immunocytofluorescence. In human sclera, BMP2, BMPR IB and BMPR II were found to be expressed in the cytomatrix of HSF, and weak signal was detected about BMPRIA.

CONCLUSION

BMP-2 and all three subtypes of BMPRs were found in HSFs and may play a role in scleral remodeling.

Effects of mechanical stimulation on viscoelasticity of rabbit scleral fibroblasts after posterior scleral reinforcement

To understand the effect of mechanical stimulation on posterior scleral reinforcement (PSR), rabbit scleral fibroblasts after PSR were subjected to stretch in vitro, and the viscoelastic behavior of scleral fibroblasts was evaluated. Three-week-old rabbits were monocularly treated by eyelid suturation randomly to prepare the experimental myopia eyes. After 60 days, the experimental myopia eyes were treated by PSR. After six months, the posterior pole scleral fibroblasts (normal sclera – group A, sclera after operation – group B and fusion region of sclera and reinforcing band – group C) were isolated and cultured in vitro. The cells were subjected to cyclic stretch regimens (sine wave, 3% and 6% elongation amplitude, 0.1 Hz, 48-h duration) by an FX-4000 Tension System. The micropipette aspiration technique was used to investigate the viscoelasticity of scleral fibroblasts. The cellular viscoelasticity ( E0, E∞ and μ) of group C was significantly lower than groups A and B ( P < 0.05), and there was no significant difference between groups A and B ( P > 0.05). The results show that the viscoelasticity in different regions of sclera after PSR is different. Following a 48-h stretch, the cellular viscoelastic parameters were significantly decreased when compared with the respective static groups ( P < 0.05) in groups A and B. For group C, the viscoelasticity of the stretch group was significantly higher than the static control group ( P < 0.05). There was no difference between the 3% and 6% stretch groups in each group ( P > 0.05). The changes of viscoelasticity suggest that different regions of sclera have different responses to mechanical stimulation in the process of treating high myopia by PSR and that mechanical stimulation plays an important role in the treatment of axial myopia by regulating the viscoelasticity of scleral fibroblasts.

Biomechanical changes in the sclera of monkey eyes exposed to chronic IOP elevations

PURPOSE

To characterize scleral biomechanics in both eyes of eight monkeys in which chronic intraocular pressure (IOP) elevation was induced in one eye.

METHODS

Each posterior sclera was mounted on a pressurization apparatus, IOP was elevated from 5 to 45 mm Hg while the 3D displacements of the scleral surface were measured by speckle interferometry. Finite element (FE) models of each scleral shell were constructed that incorporated stretch-induced stiffening and multidirectionality of the collagen fibers. FE model predictions were then iteratively matched to experimental displacements to extract unique sets of scleral biomechanical properties.

RESULTS

For all eyes, the posterior sclera exhibited inhomogeneous, anisotropic, nonlinear biomechanical behavior. Biomechanical changes caused by chronic IOP elevation were complex and specific to each subject. Specifically: (1) Glaucomatous eyes in which the contralateral normal eyes displayed large modulus or thickness were less prone to biomechanical changes; (2) glaucomatous scleral modulus associated with an IOP of 10 mm Hg decreased (when compared with that of the contralateral normal) after minimal chronic IOP elevation; (3) glaucomatous scleral modulus associated with IOPs of 30 and 45 mm Hg increased (when compared with that of the contralateral normal) after moderate IOP elevation; and (4) FE-based estimates of collagen fiber orientation demonstrated no change in the glaucomatous eyes.

CONCLUSIONS

Significant stiffening of the sclera follows exposure to moderate IOP elevations in most eyes. Scleral hypercompliance may precede stiffening or be a unique response to minimal chronic IOP elevation in some eyes. These biomechanical changes are likely to be the result of scleral extracellular matrix remodeling.

Scleral biomechanics in the aging monkey eye

PURPOSE

To investigate the age-related differences in the inhomogeneous, anisotropic, nonlinear biomechanical properties of posterior sclera from old (22.9 +/- 5.3 years) and young (1.5 +/- 0.7 years) rhesus monkeys.

METHODS

The posterior scleral shell of each eye was mounted on a custom-built pressurization apparatus, then intraocular pressure (IOP) was elevated from 5 to 45 mm Hg while the 3D displacements of the scleral surface were measured with speckle interferometry. Each scleral shell's geometry was digitally reconstructed from data generated by a 3-D digitizer (topography) and 20-MHz ultrasound (thickness). An inverse finite element (FE) method incorporating a fiber-reinforced constitutive model was used to extract a unique set of biomechanical properties for each eye. Displacements, thickness, stress, strain, tangent modulus, structural stiffness, and preferred collagen fiber orientation were mapped for each posterior sclera.

RESULTS

The model yielded 3-D deformations of posterior sclera that matched well with those observed experimentally. The posterior sclera exhibited inhomogeneous, anisotropic, nonlinear mechanical behavior. The sclera was significantly thinner (P = 0.038) and tangent modulus and structural stiffness were significantly higher in old monkeys (P < 0.0001). On average, scleral collagen fibers were circumferentially oriented around the optic nerve head (ONH). No difference was found in the preferred collagen fiber orientation and fiber concentration factor between age groups.

CONCLUSIONS

Posterior sclera of old monkeys is significantly stiffer than that of young monkeys and is therefore subject to higher stresses but lower strains at all levels of IOP. Age-related stiffening of the sclera may significantly influence ONH biomechanics and potentially contribute to age-related susceptibility to glaucomatous vision loss.

Mechanotransduction gone awry

Cells sense their physical surroundings through mechanotransduction - that is, by translating mechanical forces and deformations into biochemical signals such as changes in intracellular calcium concentration or by activating diverse signalling pathways. In turn, these signals can adjust cellular and extracellular structure. This mechanosensitive feedback modulates cellular functions as diverse as migration, proliferation, differentiation and apoptosis, and is crucial for organ development and homeostasis. Consequently, defects in mechanotransduction - often caused by mutations or misregulation of proteins that disturb cellular or extracellular mechanics - are implicated in the development of various diseases, ranging from muscular dystrophies and cardiomyopathies to cancer progression and metastasis.

Effects of cyclic mechanical stretch on extracellular matrix synthesis by human scleral fibroblasts

In order to understand the effect of mechanical strain on scleral extracellular matrix remodeling, human scleral fibroblasts were subjected to equibiaxial stretch in vitro and the expression of proteoglycans, metalloproteinases (MMPs) and tissue inhibitor of metalloproteinase-2 (TIMP-2) were evaluated. Isolated human scleral fibroblasts were seeded onto flexible bottom culture plates, and subjected to a cyclic stretch regimen of 15% equibiaxial stretch for 45 s followed by 15s of rest for 6-48 h in the presence of 35SO4. Newly synthesized proteoglycans were measured in the medium by CPC precipitation of radiolabelled glycosaminoglycans. MMP-2 activity and expression levels were measured in the medium by, Western blot, gel zymography and real-time PCR. Steady state levels of TIMP-2 mRNA and membrane-type MMP, MT1-MMP (MMP-14) mRNA were measured in the cell layer using real-time PCR. The predominant gelatinolytic enzyme secreted by scleral fibroblasts was the pro-enzyme form of MMP-2 (ProMMP-2). Mechanical stretch resulted in a significant increase of ProMMP-2 after 12 and 48 h (+76.28%, p<0.05; +19.56%, p<0.01, respectively). Mechanical stretch significantly increased the production of the active form of MMP-2 (ActiveMMP-2) after 48 h (+59.72%, p<0.05) and decreased levels of TIMP-2 mRNA (-22%, p<0.05). The rate of scleral proteoglycan synthesis and the steady state levels of MMP-2 and MMP-14 mRNA were not significantly affected by mechanical stretch. These results suggest that mechanical strain stimulates the activation of MMP-2 by scleral fibroblasts, possibly through increased levels of ProMMP-2 and reduced levels of TIMP-2. Increased levels of ActiveMMP-2 in the sclera would be expected to contribute to scleral extracellular matrix degradation, scleral thinning and possible ocular ectasia.

PI3K signaling and miRNA expression during the response of quiescent human fibroblasts to distinct proliferative stimuli

Global transcriptional profiling of human fibroblasts from two different tissue sources reveals distinct as well as conserved responses to different growth stimuli.

Background

Serum treatment of quiescent human dermal fibroblasts induces proliferation, coupled with a complex physiological response that is indicative of their normal role in wound-healing. However, it is not known to what extent such complex transcriptional events are specific to a given cell type and signal, and how these global changes are coordinately regulated. We have profiled the global transcriptional program of human fibroblasts from two different tissue sources to distinct growth stimuli, and identified a striking conservation in their gene-expression signatures.

Results

We found that the wound-healing program of gene expression was not specific to the response of dermal fibroblasts to serum but was regulated more broadly. However, there were specific differences among different stimuli with regard to signaling pathways that mediate these transcriptional programs. Our data suggest that the PI3-kinase pathway is differentially involved in mediating the responses of cells to serum as compared with individual peptide growth factors. Expression profiling indicated that let7 and other miRNAs with similar expression profiles may be involved in regulating the transcriptional program in response to proliferative signals.

Conclusion

This study provides insights into how different stimuli use distinct as well as conserved signaling and regulatory mechanisms to mediate genome-wide transcriptional reprogramming during cell proliferation. Our results indicate that conservation of transcriptional programs and their regulation among different cell types may be much broader than previously appreciated.

Mechanosensitivity and the eye: cells coping with the pressure

The cells of the various organ systems in humans are subject to mechanical forces to which they must respond. Here the authors review what is known of the ways in which the cells of animals, ranging from the prokaryotic to humans, sense and transduce mechanical forces to respond to such stimuli. In what way this pertains to the eye, especially with respect to axial myopia and the pressure related disease of glaucoma, is then surveyed.

Inhibition of human embryonic stem cell differentiation by mechanical strain

Mechanical forces have been reported to induce proliferation and/or differentiation in many cell types, but the role of mechanotransduction during embryonic stem cell fate decisions is unknown. To ascertain the role of mechanical strain in human embryonic stem cell (hESC) differentiation, we measured the rate of hESC differentiation in the presence and absence of biaxial cyclic strain. Above a threshold of 10% cyclic strain, applied to a deformable elastic substratum upon which the hESC colonies were cultured, hESC differentiation was reduced and self-renewal was promoted without selecting against survival of differentiated or undifferentiated cells. Frequency of mechanical strain application had little effect on extent of differentiation. hESCs cultured under cyclic strain retained pluripotency, evidenced by their ability to differentiate to cell lineages in all three germ layers. Mechanical inhibition of hESC differentiation could not be traced to secretion of chemical factors into the media suggesting that mechanical forces may directly regulate hESC differentiation. Mechanical strain is not sufficient to inhibit differentiation, however, in unconditioned medium, hESCs grown under strain differentiated at the same rate as cells cultured in the absence of strain. Thus, while mechanical forces play a role in regulating hESC self-renewal and differentiation, they must act synergistically with chemical signals. These findings imply that application of mechanical forces may be useful, in combination with chemical and matrix-encoded signals, towards controlling differentiation of hESCs for therapeutic applications.

Cyr61 mediates the expression of VEGF, alphav-integrin, and alpha-actin genes through cytoskeletally based mechanotransduction mechanisms in bladder smooth muscle cells

Application of cyclic strain to bladder smooth muscle (SM) cells results in profound alterations of the histomorphometry, phenotype, and function of the cells. The onset of this process is characterized by the activation of a cascade of signaling events coupled to progressive and, perhaps, interdependent changes of gene expression. In particular, externally applied cyclic stretch to cultured bladder SM cells results in the transient expression of the Cyr61 gene that encodes a cysteine-rich heparin-binding protein originally described as a proangiogenic factor capable of altering the gene programs for angiogenesis, adhesion, and extracellular matrix synthesis. In this study, we investigated the effects of mechanical stretch-induced Cyr61 on the expression of potential mechanosensitive Cyr61 target genes and the signaling pathways involved. We showed that suppression of Cyr61 expression with an adenoviral vector encoding an antisense oligonucleotide reduced mechanical strain-induced VEGF, alpha(v)-integrin, and SM alpha-actin gene expression but had no effect on the myosin heavy chain isoforms SM-1 and SM-2. Signaling pathways involving RhoA GTPase, phosphatidyl inositol 3-kinase, and cytoskeletal actin dynamics altered stretch-induced Cyr61 and Cyr61 target genes. Reciprocally, adenovirus-mediated overexpression of Cyr61 in cells cultured under static conditions increased the expression of VEGF, alpha(v)-integrin, and SM alpha-actin, as well as that of SM-1 and SM-2 isoforms, suggesting that the effects of a sustained expression of Cyr61 extend to SM specific contractile function. These effects were dependent on integrity of the actin cytoskeleton. Together, these results indicate that Cyr61 is an important determinant of the genetic reprogramming that occurs in mechanically challenged cells.