Protection of injured retinal ganglion cell dendrites and unfolded protein response resolution after long-term dietary resveratrol

Long-term dietary supplementation with resveratrol protects against cardiovascular disease, osteoporesis, and metabolic decline. This study determined how long-term dietary resveratrol treatment protects against retinal ganglion cell (RGC) dendrite loss after optic nerve injury and alters the resolution of the unfolded protein response. Associated changes in markers of endoplasmic reticulum stress in RGCs also were investigated. Young-adult Thy1-yellow fluorescent protein (YFP) and C57BL/6 mice received either control diet or diet containing resveratrol for approximately 1 year. Both groups then received optic nerve crush (ONC). Fluorescent RGC dendrites in the Thy1-YFP mice were imaged weekly for 4 weeks after ONC. There was progressive loss of dendrite length in all RGC types within the mice that received control diet. Resveratrol delayed loss of dendrite complexity and complete dendrite loss for most RGC types. However, there were variations in the rate of retraction among different RGC types. Three weeks after ONC, cytoplasmic binding immunoglobulin protein (BiP) suppression observed in control diet ganglion cell layer neurons was reversed in mice that received resveratrol, nuclear C/EBP homologous protein (CHOP) was near baseline in control diet eyes but was moderately increased by resveratrol; and increased nuclear X-box-binding protein-1 (XBP-1) observed in control diet eyes was reduced in eyes that received resveratrol to the same level as in control diet uncrushed eyes. These results indicate that protection of dendrites by resveratrol after ONC differs among RGC types and suggest that alterations in long-term expression of binding immunoglobulin protein, CHOP, and XBP-1 may contribute to the resveratrol-mediated protection of RGC dendrites after ONC.

Protection by an oral disubstituted hydroxylamine derivative against loss of retinal ganglion cell differentiation following optic nerve crush

Thy-1 is a cell surface protein that is expressed during the differentiation of retinal ganglion cells (RGCs). Optic nerve injury induces progressive loss in the number of RGCs expressing Thy-1. The rate of this loss is fastest during the first week after optic nerve injury and slower in subsequent weeks. This study was undertaken to determine whether oral treatment with a water-soluble N-hydroxy-2,2,6,6-tetramethylpiperidine derivative (OT-440) protects against loss of Thy-1 promoter activation following optic nerve crush and whether this effect targets the earlier quick phase or the later slow phase. The retina of mice expressing cyan fluorescent protein under control of the Thy-1 promoter (Thy1-CFP mice) was imaged using a blue-light confocal scanning laser ophthalmoscope (bCSLO). These mice then received oral OT-440 prepared in cream cheese or dissolved in water, or plain vehicle, for two weeks and were imaged again prior to unilateral optic nerve crush. Treatments and weekly imaging continued for four more weeks. Fluorescent neurons were counted in the same defined retinal areas imaged at each time point in a masked fashion. When the counts at each time point were directly compared, the numbers of fluorescent cells at each time point were greater in the animals that received OT-440 in cream cheese by 8%, 27%, 52% and 60% than in corresponding control animals at 1, 2, 3 and 4 weeks after optic nerve crush. Similar results were obtained when the vehicle was water. Rate analysis indicated the protective effect of OT-440 was greatest during the first two weeks and was maintained in the second two weeks after crush for both the cream cheese vehicle study and water vehicle study. Because most of the fluorescent cells detected by bCSLO are RGCs, these findings suggest that oral OT-440 can either protect against or delay early degenerative responses occurring in RGCs following optic nerve injury.

Brimonidine protects against loss of Thy-1 promoter activation following optic nerve crush

BACKGROUND

The loss of RGCs expressing Thy-1 after optic nerve injury has an initial phase of rapid decline followed by a longer phase with slower reduction rate. This study used longitudinal retinal imaging of mice expressing cyan fluorescent protein under control of the Thy-1 promoter (Thy1-CFP mice) to determine how the α2-adrenergic agonist brimonidine influences loss of Thy1 promoter activation.

METHODS

Baseline images of the fluorescent retinal neurons in 30 Thy1-CFP mice were obtained using a modified confocal scanning laser ophthalmoscope. Next, brimonidine (100 ug/kg, IP) was administered either one time immediately after optic nerve crush, or immediately after optic nerve crush and then every 2 days for four weeks. A control group received a single saline injection immediately after optic nerve crush. All animals were imaged weekly for four weeks after optic nerve crush. Loss of fluorescent retinal neurons within specific retinal areas was determined by counting.

RESULTS

At one week after optic nerve crush, the proportion of fluorescent retinal neurons retaining fluorescence was 44±7% of baseline in control mice, 51±6% after one brimonidine treatment, and 55±6% after brimonidine treatment every other day (P<0.05 for both brimonidine treatment groups compared to the control group). Subsequently, the number of fluorescent retinal neurons in the group that received one treatment differed insignificantly from the control group. In contrast, the number of fluorescent retinal neurons in the group that received repeated brimonidine treatments was greater than the control group by 28% at two weeks after crush and by 32% at three weeks after crush (P<0.05 at both time points). Rate analysis showed that brimonidine slowed the initial rate of fluorescent cell decline in the animals that received multiple treatments (P<0.05). Differences in the rate of loss among the treatment groups were insignificant after the second week.

CONCLUSION

Repeated brimonidine treatments protect against loss of fluorescence within fluorescent retinal neurons of Thy1-CFP mice after optic nerve crush. As most of fluorescent retinal neurons in this system are RGCs, these findings indicate that repeated brimonidine treatments may protect RGC health following optic nerve crush.

Ocular integrity following manganese labeling of the visual system for MRI

Injection of manganese into the eye will enhance the contrast of visual system neuronal pathways imaged by MRI (MEMRI). The present study was undertaken to determine the effect of a range of MnCl2 doses upon the integrity of various ocular structures. Anesthetized mice received ocular anterior chamber injections of 50-500 nmol of MnCl2. One week later, the eyes were fixed, embedded in paraffin, sectioned, and stained with hematoxylin and eosin. Additional animals received 50 nmol of MnCl2 injected into the anterior chamber and were later imaged using T1-weighted 7T MRI. Following 500 and 300nmol MnCl2, the corneal stroma and endothelium were degenerated, the anterior chamber contained a dense fibrin matrix with extensive inflammatory cell infiltration, a plaque often formed on the anterior lens, and significant retinal degeneration was observed. Following 100nmol MnCl2, retinal preservation of ocular structures was significantly better than at higher doses. In addition, there was no difference from vehicle control retina in cell counts within the ganglion cell layer, or in the width of the inner nuclear layer or outer nuclear layer. Also, there was no difference in the thickness of the inner plexiform layer. However, there was thinning of the peripheral outer plexiform layer, as well as in the outer segment layer. Visual system elements labeled in MRI of mice that received 100nmol MnCl2 included the retina, optic nerve, lateral geniculate nucleus, and superior colliculus. The preservation of ganglion cell layer cell counts and inner plexiform layer thickness following 100nmol MnCl2 suggests there was negligible injury to RGCs following this dose. These results support using 100nmol MnCl2 in mouse eyes for in vivo assessment of the integrity of RGC projections to target neurons in the brain.

Inhibition of histone deacetylases 1 and 3 protects injured retinal ganglion cells

PURPOSE

Thy-1 is a marker of retinal ganglion cell (RGC) differentiation. Optic nerve injury triggers reduction of Thy-1 promoter activation followed by retinal ganglion cell (RGC) death. This study determined whether MS-275, an inhibitor of the histone deacetylases 1 and 3, can inhibit these changes.

METHODS

Mice expressing cyan fluorescent protein (CFP) under control of the Thy-1 promoter received MS-275 (subcutaneous) or vehicle three times per week starting 1 week before optic nerve crush and continuing for 6 weeks. The same retinal area was imaged using the blue-light confocal scanning laser ophthalmoscope before and after optic nerve crush every week, and fluorescent spots were counted manually. The eyes were then processed for histopathologic analysis.

RESULTS

The mean proportions of fluorescent retinal neurons remaining in the vehicle group following optic nerve crush were 36 ± 8, 18 ± 6, 13 ± 10, 12 ± 4, 13 ± 5, and 13 ± 5% at weeks 1 through 6, respectively (n = 6). In contrast, the mean proportions of fluorescent retinal neurons remaining in the group treated with MS-275 were 59 ± 19, 39 ± 11, 34 ± 12, 33 ± 15, 32 ± 13, and 27 ± 15% at weeks 1 through 6, respectively (n = 7, P < 0.05 at weeks 1 through 5). Rate analysis showed that MS-275 slowed the rate of loss during the first 2 weeks by 23% (P < 0.05) and subsequently was similar. Histopathologic analysis revealed 27 ± 13% greater ganglion cell layer (GCL) neurons in the eyes from mice that received MS-275 treatment (P < 0.02).

CONCLUSIONS

These results indicate that treatment with MS-275 protects against the loss of RGC differentiation and promotes RGC survival following optic nerve injury.

Brimonidine blocks glutamate excitotoxicity-induced oxidative stress and preserves mitochondrial transcription factor a in ischemic retinal injury

Glutamate excitotoxicity-induced oxidative stress have been linked to mitochondrial dysfunction in retinal ischemia and optic neuropathies including glaucoma. Brimonindine (BMD), an alpha 2-adrenergic receptor agonist, contributes to the neuroprotection of retinal ganglion cells (RGCs) against glutamate excitotoxicity or oxidative stress. However, the molecular mechanisms of BMD-associated mitochondrial preservation in RGC protection against glutamate excitotoxicity-induced oxidative stress following retinal ischemic injury remain largely unknown. Here, we tested whether activation of alpha 2 adrenergic receptor by systemic BMD treatment blocks glutamate excitotoxicity-induced oxidative stress, and preserves the expression of mitochondrial transcription factor A (Tfam) and oxidative phosphorylation (OXPHOS) complex in ischemic retina. Sprague-Dawley rats received BMD (1 mg/kg/day) or vehicle (0.9% saline) systemically and then transient ischemia was induced by acute intraocular pressure elevation. Systemic BMD treatment significantly increased RGC survival at 4 weeks after ischemia. At 24 hours, BMD significantly decreased Bax expression but increased Bcl-xL and phosphorylated Bad protein expression in ischemic retina. Importantly. BMD significantly blocked the upregulations of N-methyl-D-aspartate receptors 1 and 2A protein expression, as well as of SOD2 protein expression in ischemic retina at 24 hours. During the early neurodegeneration following ischemic injury (12–72 hours), Tfam and OXPHOS complex protein expression were significantly increased in vehicle-treated retina. At 24 hours after ischemia, Tfam immunoreactivity was increased in the outer plexiform layer, inner nuclear layer, inner plexiform layer and ganglion cell layer. Further, Tfam protein was expressed predominantly in RGCs. Finally, BMD preserved Tfam immunoreactivity in RGCs as well as Tfam/OXPHOS complex protein expression in the retinal extracts against ischemic injury. Our findings suggest that systemic BMD treatment protects RGCs by blockade of glutamate excitotoxicity-induced oxidative stress and subsequent preservation of Tfam/OXPHOS complex expression in ischemic retina.

A new vicious cycle involving glutamate excitotoxicity, oxidative stress and mitochondrial dynamics

Glutamate excitotoxicity leads to fragmented mitochondria in neurodegenerative diseases, mediated by nitric oxide and S-nitrosylation of dynamin-related protein 1, a mitochondrial outer membrane fission protein. Optic atrophy gene 1 (OPA1) is an inner membrane protein important for mitochondrial fusion. Autosomal dominant optic atrophy (ADOA), caused by mutations in OPA1, is a neurodegenerative disease affecting mainly retinal ganglion cells (RGCs). Here, we showed that OPA1 deficiency in an ADOA model influences N-methyl-D-aspartate (NMDA) receptor expression, which is involved in glutamate excitotoxicity and oxidative stress. Opa1(enu/+) mice show a slow progressive loss of RGCs, activation of astroglia and microglia, and pronounced mitochondrial fission in optic nerve heads as found by electron tomography. Expression of NMDA receptors (NR1, 2A, and 2B) in the retina of Opa1(enu/+) mice was significantly increased as determined by western blot and immunohistochemistry. Superoxide dismutase 2 (SOD2) expression was significantly decreased, the apoptotic pathway was activated as Bax was increased, and phosphorylated Bad and BcL-xL were decreased. Our results conclusively demonstrate that not only glutamate excitotoxicity and/or oxidative stress alters mitochondrial fission/fusion, but that an imbalance in mitochondrial fission/fusion in turn leads to NMDA receptor upregulation and oxidative stress. Therefore, we propose a new vicious cycle involved in neurodegeneration that includes glutamate excitotoxicity, oxidative stress, and mitochondrial dynamics.

A selective inhibitor of drp1, mdivi-1, increases retinal ganglion cell survival in acute ischemic mouse retina

PURPOSE

To determine whether acute intraocular pressure (IOP) elevation alters dynamin-related protein 1 (Drp1) as well as whether a selective inhibitor of Drp1, mdivi-1, can block apoptotic cell death and subsequently increase retinal ganglion cell (RGC) survival in ischemic mouse retina.

METHODS

C57BL/6 mice received injections of mdivi-1 (50 mg/kg) or vehicle, and then transient retinal ischemia was induced by acute IOP elevation. RGC survival was measured after FluoroGold labeling. Drp1 and glial fibrillary acidic protein (GFAP) protein expression and distribution were assessed at 12 hours after ischemia-reperfusion by Western blot and immunohistochemistry. Apoptotic cell death was assessed by TUNEL staining.

RESULTS

Drp1 and GFAP protein expression was significantly increased in the early neurodegenerative events (within 12 hours) of ischemic mouse retina. Mdivi-1 treatment blocked apoptotic cell death in ischemic retina, and significantly increased RGC survival at 2 weeks after ischemia. In the normal mouse retina, Drp1 is expressed in the ganglion cell layer (GCL) as well as the inner plexiform layer, the inner nuclear layer (INL), and the outer plexiform layer (OPL). In the GCL, Drp1 immunoreactivity was strong in RGCs. While Drp1 protein expression was increased in the GCL of vehicle-treated ischemic retina at 12 hours. Mdivi-1 treatment did not change this increase of Drp1 protein expression but significantly decreased GFAP protein expression.

CONCLUSIONS

These findings suggest that altered Drp1 activity after acute IOP elevation may be an important component of a biochemical cascade leading to RGC death in ischemic retina.

Inducible nitric oxide synthase-mediated alteration of mitochondrial OPA1 expression in ocular hypertensive rats

PURPOSE

To investigate how OPA1 expression and distribution are altered by increased nitric oxide (NO) and whether aminoguanidine, a relative selective NO synthase (NOS)-2 inhibitor, can restore OPA1 expression and subsequently increase retinal ganglion cell (RGC) survival in ocular hypertensive rats.

METHODS

Elevated intraocular pressure was induced unilaterally by translimbal laser photocoagulation of the trabecular meshwork in Sprague-Dawley rats. Aminoguanidine (100 mg/kg) was administered by intraperitoneal injection for 3 consecutive days in rats after laser treatment. Preservation of fluorochrome-labeled RGCs was assessed 2 weeks later. GFAP, NOS-2, or OPA1 protein expression and distribution were assessed by Western blot analysis and immunohistochemistry. OPA1 mRNA was measured by qPCR.

RESULTS

OPA1 mRNA and protein expression were significantly increased in the vehicle-treated hypertensive rat retina. Aminoguanidine treatment significantly reduced expression of the 90- and 65-kDa OPA1 isoforms but did not significantly change the 80-kDa OPA1 isoform in hypertensive retina. In addition, the increases in NOS-2 and GFAP protein expression were blocked by aminoguanidine treatment in the hypertensive retina. NOS-2 immunoreactivity was induced in cells of the ganglion cell layer in the vehicle-treated hypertensive retina. Aminoguanidine treatment significantly increased RGC survival at 2 weeks after IOP elevation.

CONCLUSIONS

Although NOS-2/NO induction may contribute to hypertensive retinal cell death, an increase in mitochondrial OPA1 may provide an important cellular defense mechanism against pressure-mediated retinal damage. These findings suggest that mitochondrial preservation after inhibition of NOS-2 may be useful for protecting RGCs against glaucomatous damage.

Increased optic atrophy type 1 expression protects retinal ganglion cells in a mouse model of glaucoma

PURPOSE

The goal of this study is to determine whether increased optic atrophy type 1 (OPA1) expression protects against retinal ganglion cell (RGC) death in glaucomatous DBA/2J mice.

METHODS

Intraocular pressure in DBA/2J mice was measured, and pre-glaucomatous DBA/2J mice eyes were transfected with recombinant adeno-associated virus serotype 2 (AAV2) constructs including AAV2-wild type (WT) mOPA1 for two months. Increased OPA1 expression was confirmed by western blotting and RGC survival was assessed by retrograde labeling with FluoroGold. In addition, apoptotic cell death and mitochondrial structure were determined in AAV2-WT mOPA1-transfected differentiated RGC-5 cells exposed to elevated hydrostatic pressure (30 mmHg) for three days.

RESULTS

WT AAV2-mOPA1 transfection significantly increased 90 kDa and 80 kDa OPA1 isoforms in the retina of glaucomatous DBA/2J mice. OPA1 immunoreactivity was increased in the inner nuclear layer, inner plexiform layer, and ganglion cell layer in nine month-old glaucomatous DBA/2J mice transfected with AAV2-WT mOPA1. Overexpression of OPA1 significantly increased RGC survival at two months after AAV2-WT mOPA1 transfection, and decreased activation of both astroglia and microglia in the retina of glaucomatous DBA/2J mice. Also, overexpression of OPA1 in differentiated RGC-5 cells resulted in less apoptotic cell death and blocked mitochondrial fission following elevated hydrostatic pressure.

CONCLUSIONS

OPA1 can directly modulate RGC survival, and increasing OPA1 expression may protect against RGC death in glaucomatous optic neuropathy.

Disruption of the podosome adaptor protein TKS4 (SH3PXD2B) causes the skeletal dysplasia, eye, and cardiac abnormalities of Frank-Ter Haar Syndrome

Frank-Ter Haar syndrome (FTHS), also known as Ter Haar syndrome, is an autosomal-recessive disorder characterized by skeletal, cardiovascular, and eye abnormalities, such as increased intraocular pressure, prominent eyes, and hypertelorism. We have conducted homozygosity mapping on patients representing 12 FTHS families. A locus on chromosome 5q35.1 was identified for which patients from nine families shared homozygosity. For one family, a homozygous deletion mapped exactly to the smallest region of overlapping homozygosity, which contains a single gene, SH3PXD2B. This gene encodes the TKS4 protein, a phox homology (PX) and Src homology 3 (SH3) domain-containing adaptor protein and Src substrate. This protein was recently shown to be involved in the formation of actin-rich membrane protrusions called podosomes or invadopodia, which coordinate pericellular proteolysis with cell migration. Mice lacking Tks4 also showed pronounced skeletal, eye, and cardiac abnormalities and phenocopied the majority of the defects associated with FTHS. These findings establish a role for TKS4 in FTHS and embryonic development. Mutation analysis revealed five different homozygous mutations in SH3PXD2B in seven FTHS families. No SH3PXD2B mutations were detected in six other FTHS families, demonstrating the genetic heterogeneity of this condition. Interestingly however, dermal fibroblasts from one of the individuals without an SH3PXD2B mutation nevertheless expressed lower levels of the TKS4 protein, suggesting a common mechanism underlying disease causation.

Outflow facility in mice with a targeted type I collagen mutation

PURPOSE

Transgenic Col1a1(r/r) mice develop elevated intraocular pressure (IOP) with an open angle and progressive optic nerve axon loss. The present study was undertaken to evaluate aqueous outflow facility and its age dependence in these mice.

METHODS

Homozygous B6;129S4-Col1a1(tm1Jae) mice and corresponding wild-type Col1a1(+/+) mice from 12 to 56 weeks of age were anesthetized, and IOP was measured with a microneedle. Outflow facility was determined by a two-level, constant-pressure infusion

METHOD

Type I collagen, subunit alpha1 was assessed in sclera and choroid by Western blot analysis.

RESULTS

The mean IOP in 12- to 36-week-old transgenic Col1a1(r/r) mice was 25.1% higher than in control Col1a1(+/+) mice (P < 0.01), whereas the mean outflow facility was 25.4% lower than in control mice (P < 0.01). After this period, the mean IOP in 42- to 56-week-old transgenic mice returned to normal levels, whereas outflow facility increased by 36.0%. Over the 12- to 56-week study period, IOP and outflow facility in the transgenic mice were inversely correlated (r(2) = -0.702, P < 0.01). Collagen I alpha1 content was greater in 37- and 43-week-old transgenic mice than in age-matched wild-type control mice.

CONCLUSIONS

Outflow facility is reduced in transgenic Col1a1(r/r) mice with IOP elevation. The inverse correlation of IOP elevation to facility reduction indicates that increased resistance in the aqueous outflow pathway contributes to ocular hypertension in Col1a1(r/r) mice. These mice may be useful as a model for open-angle glaucoma, as well as for assessing the relationship between collagen type I metabolism and aqueous outflow.

Partitioning of the aqueous outflow in rat eyes

PURPOSE

To determine the effect of molecular size on the drainage route of dextrans injected into the rat anterior chamber (AC).

METHODS

Anesthetized adult rats received monocular AC injections of a mixture of 3-kDa dextran-cascade blue, 40-kDa dextran-Texas red, and 500-kDa dextran-FITC. After exsanguination of the rats 2, 4, 6, 12, 24, or 72 hours later, the eyes, facial lymph nodes, and cervical lymph nodes were isolated, and the total content of each dextran type was determined by spectrofluorometry. Also, lymph nodes were evaluated histologically 4 and 24 hours after AC injection of 40-kDa dextran-FITC.

RESULTS

The speed of tracer exit from the eye varied with 3-kDa dextran > 40-kDa dextran > 500-kDa dextran. No 3-kDa dextran was detected in either facial lymph nodes or cervical lymph nodes at any time point. The average recovery of 40-kDa dextran in the facial and cervical lymph nodes peaked at 52.6% of the amount injected. In contrast, average recovery of 500-kDa dextran in the facial and cervical lymph nodes peaked at 1.8% of amount the injected. Histology showed 40-kDa dextran was mostly contained within lymph node cells at both 4 and 24 hours after injection.

CONCLUSIONS

Transport of 40-kDa dextran from the AC to the facial lymph nodes and cervical lymph nodes is markedly more efficient than that of 500-kDa dextran. In contrast, there is negligible transport of 3-kDa dextran. These results demonstrate that different sized aqueous macromolecules can exit the eye by different routes.

Episcleral venous pressure of mouse eye and effect of body position

PURPOSE

To measure the episcleral venous pressure (EVP) of the mouse eye and to investigate the effect of body position on EVP and intraocular pressure (IOP).

METHODS

A microneedle connected to a pressure transducer was used to measure IOP in NIH Swiss white mice. To measure EVP, a reservoir connected to this transducer allowed modulation of the intracameral pressure by changing its height. As intracameral pressure was gradually lowered, there was an observable reflux of erythrocytes from an episcleral vein into Schlemm's canal. The IOP at which this occurred was the endpoint of the EVP measurement. EVP and IOP were measured in a horizontal body position (0 degrees ) analogous to an awake mouse and at 30 degrees and 60 degrees head-down body position from the horizontal position. EVP was measured twice in each eye of 6 mice.

RESULTS

Mean IOP at 0 degrees, 30 degrees and 60 degrees of head-down position was 16.5 +/- 0.6, 18.2 +/- 0.6, and 19.5 +/- 1.8 mmHg, respectively. EVP (horizontal) was 9.6 +/- 1.3 mmHg (N = 6 eyes). EVP significantly increased with increasing degree of head-down position (SNK test, p < 0.05). EVP at 30 degrees and 60 degrees of head-down position was 11.2 +/- 1.3 and 13.3 +/- 1.5 mmHg, respectively.

CONCLUSIONS

Mouse EVP was successfully measured based on the detection of erythrocyte reflux from an episcleral vein into Schlemm's canal. Both EVP and IOP increased with the degree of the head-down body position.

Longitudinal profile of retinal ganglion cell damage assessed with blue-light confocal scanning laser ophthalmoscopy after ischaemic reperfusion injury

AIM

To longitudinally investigate retinal ganglion cell (RGC) expression of Thy-1, a cell-surface glycoprotein specifically expressed in RGCs, with a blue-light confocal scanning laser ophthalmoscope, following retinal ischaemia induced by acute elevation of intraocular pressure.

METHODS

A blue-light confocal scanning laser ophthalmoscope (bCSLO, 460 nm excitation and 490 nm detection) was used to image Thy1-cyan fluorescent protein (CFP) mice before and weekly for 4 weeks after transiently elevating the intraocular pressure to 115 mm Hg for 45 min (n = 4) or 90 min (n = 5) to induce ischaemic injury. Corresponding retinal areas before and after the intraocular pressure (IOP) elevation, during the period of ischaemic reperfusion, were compared, and the fluorescent spots (Thy-1 expressing RGCs) were counted. The longitudinal profile of CFP-expressing RGCs was modelled with a linear regression equation. The spatial distribution of RGC damage was analysed in the superior, nasal, inferior and temporal quadrants of the retina.

RESULTS

No significant change was found at 4 weeks after 45 min of IOP elevation (n = 4, p = 0.465). The average RGC densities before and 4 weeks after IOP elevation were 1660 (SD 242) cells/mm2 and 1624 (209) cells/mm2, respectively. However, significant loss of CFP-expressing RGCs was detected at 1 week following 90 min of IOP elevation (n = 5, p<0.001). After this initial RGC loss, no significant change was detected subsequently. The proportion of RGC fluorescence remaining was variable and ranged from 14.5% to 79.5% at 4 weeks after the IOP elevation. The average RGC densities before and 4 weeks after IOP elevation were 1443 (162) cells/mm2 and 680 (385) cells/mm2, respectively. Diffuse loss of fluorescent RGCs was observed in the spatial distribution analysis.

CONCLUSIONS

The longitudinal profile of Thy-1 expressing RGC fluorescence loss after ischaemic injury is non-progressive and unrelated to the duration of reperfusion.

Memantine blocks mitochondrial OPA1 and cytochrome c release and subsequent apoptotic cell death in glaucomatous retina

PURPOSE

To determine whether intraocular pressure (IOP) elevation alters OPA1 expression and triggers OPA1 release, as well as whether the uncompetitive N-methyl-d-aspartate (NMDA) glutamate receptor antagonist memantine blocks OPA1 release and subsequent apoptotic cell death in glaucomatous DBA/2J mouse retina.

METHODS

Preglaucomatous DBA/2J mice received memantine (5 mg/kg, intraperitoneal injection, twice daily for 3 months) and IOP in the eyes was measured monthly. RGC loss was counted after FluoroGold labeling. OPA1, Dnm1, Bcl-2, and Bax mRNA were measured by qPCR. OPA1 protein was assessed by immunohistochemistry and Western blot. Apoptotic cell death was assessed by TUNEL staining.

RESULTS

Memantine treatment significantly increased RGC survival in glaucomatous DBA/2J mice and increased the 75-kDa OPA1 isoform, but did not alter the 80- and 90-kDa isoforms. The isoforms of OPA1 were significantly increased in the cytosol of the vehicle-treated glaucomatous retinas but were significantly decreased in memantine-treated glaucomatous retinas. OPA1 immunoreactivity was decreased in the photoreceptors of both vehicle- and memantine-treated glaucomatous retinas, but was increased in the outer plexiform layer of only the memantine-treated glaucomatous retinas. Memantine blocked apoptotic cell death in the GCL, increased Bcl-2 gene expression, and decreased Bax gene expression.

CONCLUSIONS

OPA1 release from mitochondria in glaucomatous mouse retina is inhibited by blockade of glutamate receptor activation. Because this OPA1 effect was accompanied by increased Bcl-2 expression, decreased Bax expression, and apoptosis blockade, glutamate receptor activation in the glaucomatous retina may involve a distinct mitochondria-mediated cell death pathway.

Glutamate receptor activation triggers OPA1 release and induces apoptotic cell death in ischemic rat retina

PURPOSE

Glutamate receptor activation-induced excitotoxicity has been hypothesized to cause retinal ganglion cell (RGC) death in glaucoma and to link mitochondrial dysfunction in both acute and chronic neurodegenerative disorders. However, the relationships among elevated intraocular pressure (IOP), glutamate receptor-mediated excitotoxicity, and mitochondrial dysfunction in glaucoma remains unknown. The goal of this study was to determine whether the N- methyl D-aspartate (NMDA) glutamate receptor antagonist MK801 can block optic atrophy 1 (OPA1) release and subsequent apoptotic cell death, as well as whether acute IOP elevation triggers OPA1 release and alters OPA1 gene and protein expression in the rat retina after ischemia.

METHODS

Sprague Dawley rats received injections of MK801 (10 mg/kg) or vehicle and then transient retinal ischemia was induced by acute IOP elevation. Following subcellular fractionation, changes in cytoplasmic and mitochondrial OPA1 were assessed by western blot analysis. Also, the expression of OPA1 mRNA was measured by Taqman qPCR, the distribution of OPA1 protein was assessed by immunohistochemistry, and apoptotic cell death was assessed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining.

RESULTS

The ~65 and 90 kDa isoforms of OPA1 were increased in the cytosol in the rat retina at 6 h and at 12 h, but only the 90 kDa isoform of OPA1 was decreased at 12 h after ischemia induced by acute IOP elevation. This suggests that ischemic insult induced OPA1 release from the mitochondria in retinas. Pretreatment with MK801 blocked this effect and significantly increased OPA1 immunoreactivity in the inner retinal layers, as well as OPA1 gene expression and total protein expression in retinas at 12 h after ischemia. Further, pretreatment with MK801 prevented apoptotic cell death in retinas at 12 h after ischemia. Following acute IOP elevation, Bcl-2 mRNA expression in retinas was decreased at 3 h and 6 h but increased at 12 h and 24 h. In contrast, Bax mRNA expression in these retinas was increased in the first 12 h and then plateaued. Moreover, pretreatment with MK801 increased Bcl-2 mRNA expression, but did not alter the course of Bax mRNA expression.

CONCLUSIONS

These results indicate that OPA1 release from mitochondria triggered by acute IOP elevation is inhibited by blockade of glutamate receptor activation. Because this effect was accompanied by increases of Bcl-2 expression, no changes of Bax expression, and blockade of apoptosis, these findings indicate that glutamate receptor activation following acute IOP elevation may lead to a distinct mitochondria-mediated cell death pathway in ischemic retina. These results support further studies to determine whether ischemia-induced OPA1 release may be an important component of the biochemical cascade leading to pressure-related ischemic damage in glaucomatous retina.

Intraocular pressure elevation induces mitochondrial fission and triggers OPA1 release in glaucomatous optic nerve

PURPOSE

To determine whether elevation of intraocular pressure (IOP) triggers mitochondrial fission and ultrastructural changes and alters optic atrophy type 1 (OPA1) expression and distribution in the optic nerve (ON) of glaucomatous DBA/2J mice.

METHODS

IOP in the eyes of DBA/2J mice was measured, and mitochondrial structural changes were assessed by conventional electron microscopy (EM) and EM tomography. Cytochrome c oxidase IV subunit 1 (COX), OPA1, and Dnm1, a rat homologue of dynamin-related protein-1, mRNA were measured by quantitative (q)PCR. COX and OPA1 protein distribution was assessed by immunocytochemistry and Western blot.

RESULTS

Excavation of the optic nerve head (ONH), axon loss, and COX reduction were evident in 10-month-old glaucomatous ONHs of eyes with >20 mm Hg IOP elevation. EM analysis showed mitochondrial fission, matrix swelling, substantially reduced cristae volume, and abnormal cristae depletion in 10-month-old glaucomatous ONH axons. The mean length of mitochondrial cross section in these axons decreased from 858.2 +/- 515.3 nm in 3-month-old mice to 583.3 +/- 298.6 nm in 10-month-old glaucomatous mice (P < 0.001). Moderate reductions of COX mRNA were observed in the 10-month-old DBA/2J mice's ONHs. Larger reductions of OPA1 immunoreactivity and gene expression were coupled with larger increases of Dnm1 gene expression in 10-month-old glaucomatous ONH. Subcellular fractionation analysis indicates increased release of both OPA1 and cytochrome c from mitochondria in 10-month-old glaucomatous ONs.

CONCLUSIONS

IOP elevation may directly damage mitochondria in the ONH axons by promoting reduction of COX, mitochondrial fission and cristae depletion, alterations of OPA1 and Dnm1 expression, and induction of OPA1 release. Thus, interventions to preserve mitochondria may be useful for protecting against ON degeneration in glaucoma.

Longitudinal profile of retinal ganglion cell damage after optic nerve crush with blue-light confocal scanning laser ophthalmoscopy

PURPOSE

To investigate the long-term longitudinal profile of retinal ganglion cell (RGC) damage after optic nerve crush with a new technique for in vivo imaging of RGCs.

METHODS

A blue-light confocal scanning laser ophthalmoscope (bCSLO; 460 nm excitation, 490 nm detection) was used to image Thy-1 CFP mice aged 6 to 9 months (n = 5) before optic nerve crush, weekly after crush for 3 weeks, and at weeks 10 and 50 after optic nerve crush. A sham procedure was performed in the contralateral eye, and it was imaged as a control. Corresponding retinal areas before and after optic nerve crush were compared, and the fluorescent spots were counted manually. The longitudinal profile of RGC degeneration was modeled and compared with one-phase and two-phase exponential decay equations.

RESULTS

A significant and progressive loss of fluorescent spots was found after optic nerve crush with 18.6% +/- 2.3%, 11.3% +/- 3.4%, 8.8% +/- 5.3%, 4.2% +/- 3.1%, and 3.3% +/- 2.1% of Thy-1-expressing RGCs remaining at weeks 1, 2, 3, 10, and 50, respectively, after optic nerve crush (P < 0.001; n = 5). There was no change in the fluorescence density in the contralateral control (P = 0.893). Two-phase exponential decay (y = 0.03 + 0.83e(-)(2.78t) + 0.14e(-)(0.30t)) was a better fit than one-phase exponential decay (y = 0.94e(-)(1.93t) + 0.06; P = 0.003) equations, with half-lives of fast phase and slow phase of 1.7 days and 16.3 days, respectively.

CONCLUSIONS

The longitudinal profile of RGC degeneration after optic nerve crush is characterized by a two-phase exponential decay model. bCSLO imaging provides an efficient and noninvasive approach to the longitudinal study of progressive RGC damage.

Effect on diurnal intraocular pressure variation of eliminating the alpha-2 adrenergic receptor subtypes in the mouse

PURPOSE

To investigate the effect on circadian variation of intraocular pressure (IOP) of eliminating the alpha2A-, alpha2B-, or the alpha2C-adrenergic receptor subtypes in the mouse.

METHODS

A microneedle method was used to measure IOP in knockout mice lacking the alpha2A-, alpha2B-, or the alpha2C-receptor (alpha2A-R(-/-), alpha2B-R(-/-), alpha2C-R(-/-)), in wild-type mice of the alpha2B knockout strain (alpha2B-R(+/+)), and in the background strain mice, C57BL/6. All mice were maintained in a 12-hour light-dark cycle commencing at 0600 hours. IOP was measured at 0900 and 2100 hours in the five groups: C57BL/6 (n = 8), alpha2A-R(-/-) (n = 10), alpha2B-R(-/-) (n = 8), alpha2B-R(+/+) (n = 8), and alpha2C-R(-/-) (n = 10). In parallel experiments, eyes from the alpha2A-R(-/-), alpha2B-R(-/-), alpha2C-R(-/-), and C57BL/6 mice were embedded in epoxy resin, and semithin sections were stained with toluidine blue.

RESULTS

IOP at 0900 hours in B6, alpha2A-R(-/-), alpha2B-R(-/-), alpha2B-R(+/+), and alpha2C-R(-/-) mice was 17.1 +/- 1.8, 17.7 +/- 1.4, 17.1 +/- 2.1, 17.6 +/- 1.3, and 17.3 +/- 0.9 mm Hg, respectively (mean +/- SD). IOP at 2100 hours in the same eyes was 19.6 +/- 1.9, 19.2 +/- 2.2, 20.5 +/- 1.5, 19.7 +/- 0.8, and 21.3 +/- 2.7 mm Hg, respectively. There was no significant difference among these genotypes in IOP measured at either time point (P > 0.05, ANOVA). Within each genotype, IOP at 2100 hours was significantly higher than IOP at 0900 hours (C57BL/6, alpha2B-R(-/-), alpha2B-R(+/+), and alpha2C-R(-/-): P < 0.01; alpha2A-R(-/-): P < 0.05, paired t-test). Differences in the diurnal IOP change among the different genotypes were insignificant (P > 0.05, ANOVA). Histopathologic assessment found minimal differences in the structural organization of the anterior segment among the alpha2A-R(-/-), alpha2B-R(-/-),alpha2C-R(-/-), or C57BL/6 mice.

CONCLUSIONS

These results indicate that IOP magnitude and circadian variation are minimally altered by the absence of the alpha2A-, alpha2B-, or alpha2C-receptor subtypes in transgenic mice.

In vivo imaging of murine retinal ganglion cells

Current methods for in vivo retinal ganglion cells (RGCs) imaging involve either retrograde or intravitreal injection of chemical or biological tracers, which are invasive and may require repeated injection for serial long-term assessment. We have developed a confocal scanning laser ophthalmoscope technique (blue-light CSLO or bCSLO) to image retinal ganglion cells (RGCs) in mice expressing cyan fluorescent protein under the control of a Thy-1 promoter. Fluorescent spots corresponding to CFP-expressing retinal ganglion cells were discernable with the bCSLO. 96.1+/-2.6% of CFP expressing cells also were retrograde labeled with DiI indicating the bCSLO imaged fluorescent spots are RGCs. The imaging of Thy-1 promoter-driven CFP expression in these mice could serve as a sensitive indicator to reflect the integrity of RGCs, and provides a non-invasive method for longitudinal study of the mechanism of RGC degeneration and the effect of neuroprotective agents.

Oxidative stress is an early event in hydrostatic pressure induced retinal ganglion cell damage

PURPOSE

To determine whether oxidative adduct formation or heme oxygenase-1 (HO-1) expression are altered in retinal ganglion cell (RGC) cultures exposed to elevated hydrostatic pressure and in a mouse model of glaucoma.

METHODS

Cultured RGC-5 cells were subjected to 0, 30, 60, or 100 mm Hg hydrostatic pressure for 2 hours, and the cells were harvested. Parallel experiments examined the recovery from this stress, the effect of direct 4-hydroxy-2-nonenal (HNE) treatment, and the effect of pretreatment with resveratrol or quercetin. Mice were anesthetized and intraocular pressure was increased to 30, 60, or 100 mm Hg for 1 hour; then the retinas were harvested. HNE adduct formation and HO-1 expression were assessed by immunocytochemistry and immunoblotting.

RESULTS

Increases of HNE-protein adducts (up to 5-fold) and HO-1 expression (up to 2.5 fold) in pressure-treated RGC-5 cells were dose dependent. During recovery experiments, HNE-protein adducts continued to increase for up to 10 hours; in contrast, HO-1 expression decreased immediately. HNE, at a concentration as low as 5 muM, led to neurotoxicity in RGC-5 cells. HNE adducts and HO-1 expression increased in the mouse retina and optic nerve after acute IOP elevation up to 5.5-fold and 2-fold, respectively. Antioxidant treatment reduced the oxidative stress level in pressure-treated RGC-5 cells.

CONCLUSIONS

This study demonstrates that oxidative stress is an early event in hydrostatic pressure/IOP-induced neuronal damage. These findings support the view that oxidative damage contributes early to glaucomatous optic neuropathy.

Prostaglandin FP Receptors Do Not Contribute to 24-hour Intraocular Pressure Variation in Mice

PURPOSE

It is not known whether the prostaglandin FP receptor plays an important role in endogenous 24-hour regulation of intraocular pressure. The purpose of this study was to compare 24-hour intraocular pressure (IOP) in FP receptor-knockout mice with that of wild-type mice that have normal FP receptor expression.

METHODS

The 24-hour IOP profile was determined by rebound tonometry in FP-knockout and wild-type mice. Peak and trough IOP was then measured by microneedle cannulation of the anterior chamber in homozygous (FP(-/-); n = 8), heterozygous (FP(+/-); n = 14), and C57BL/6 background strain mice (FP(+/+); n = 11). To confirm any differences in baseline IOP between genotypes, midafternoon IOP was also measured in a larger, separate group of FP(-/-) mice (n = 20), FP(+/-) mice (n = 49), and FP(+/+) (n = 23) wild-type littermates.

RESULTS

Trough IOPs were measured between 10 AM and 12 PM, peak IOPs were measured between 8 and 10 PM. For FP(+/+), FP(+/-), and FP(-/-) mice trough IOP was 16.2, 15.3, and 15.1 mm Hg and peak IOPs were 18.2, 18.4, and 17.7 mm Hg, respectively. There was no significant difference among genotypes for mean peak or mean trough IOP or for peak-trough difference in IOP among genotypes (P > 0.05, ANOVA). In addition, there was no significant difference in midafternoon IOP between genotypes in a larger population (n = 92) of FP-knockout and wild-type mice.

CONCLUSIONS

An intact FP receptor does not appear to be critical for normal 24-hour IOP regulation in the mouse eye.

Elevated hydrostatic pressure triggers mitochondrial fission and decreases cellular ATP in differentiated RGC-5 cells

PURPOSE

Mitochondrial fission is a cellular response to stress that has an important role in neuronal cell death in neurodegenerative diseases. The purpose of this study was to determine whether elevated hydrostatic pressure induces mitochondrial fission and dysfunction in cultured retinal ganglion cells.

METHODS

RGC-5 cells were differentiated with succinyl concanavalin A (50 microg/mL) and transferred to a pressurized incubator in which 30 mm Hg of pressure was applied for 1, 2, or 3 days. As a control, differentiated cells from an identical passage were incubated simultaneously in a conventional incubator at each of the time points. Live RGC-5 cells were then labeled with a red fluorescent mitochondrial dye and mitochondrial morphology was assessed by fluorescence microscopy and electron microscopy. After elevated hydrostatic pressure, the cellular adenosine triphosphate (ATP) levels were also measured by a luciferase-based assay.

RESULTS

Mitochondrial fission, characterized by the conversion of tubular fused mitochondria into isolated small organelles, was triggered in >74.3% +/- 1.9% of mitochondria at 3 days after elevated hydrostatic pressure. Only 4.7% +/- 1.4% of nonpressurized control cells displayed mitochondrial fission after 3 days. Electron microscopy showed that elevated hydrostatic pressure for 3 days induced abnormal cristae depletion and decreased the length of the mitochondria. On elevation of hydrostatic pressure, the fission-linked protein, Drp-1 was translocated from the cytosol to the mitochondria. Elevated hydrostatic pressure also resulted in a significant, time-dependent reduction of cellular ATP.

CONCLUSIONS

Elevated hydrostatic pressure triggered mitochondrial fission, abnormal cristae depletion, Drp-1 translocation, and cellular ATP reduction in differentiated RGC-5 cells. Increased understanding of the molecular mechanisms that regulate the cellular response to elevated pressure including mitochondrial fission may provide new therapeutic targets for protecting RGCs from elevated hydrostatic pressure.

Impact of donor and recipient factors on allograft survival in lung transplantation: A single-center analysis

BACKGROUND

It remains unclear which donor and recipient factors influence long-term allograft function in lung transplantation (LTx).

METHODS

From October 1988 to February 2005, a total of 280 recipients underwent LTx at our center. Donor data and cause of death (CoD) were analyzed. The CoD was categorized according to rate of increase in intracranial pressure at the time of death. Each donor and recipient factor was correlated with long-term graft function. Recipient details, type of transplant, indication for transplant, and time on waiting list were analyzed. Recipients were stratified based on allograft ischemia time (AIT): 0 to 6, 6 to 8, 8 to 10, and >10 hours.

RESULTS

Mean donor age was 30.9 years (36.7% male); 49.8% were cytomegalovirus (CMV) positive. Donor CoD was characterized by a slow rise in intracranial pressure (ICP) in 34.4%, rapid ICP in 18.7%, an intermediate ICP in 44.3%, and with no rise in 2.6%. A graft survival benefit was seen with female donors (P = .048); 34.4% of recipients ultimately developed graft failure at long term follow-up. Mean recipient age was 48 years; 63% were male and mean body-mass index (BMI) was 23.6; 60.2% had single lung transplantation, and mean wait list time was 323 days. Mean AIT totaled 421 minutes. Graft survival was longer with AIT of 8 to 10 hours compared to 6 to 8 hours (P = .03).

CONCLUSIONS

Donor factor analysis implied only female donor status conferred a long-term graft survival advantage. Intracranial pressure rise differences appear clinically unimportant. Prolonged cold ischemic time (>10 hours) or low recipient BMI did not adversely affect allograft function in our review.

Direct Matrix Metalloproteinase Enhancement of Transscleral Permeability

PURPOSE

Previous studies have shown that increased trans-scleral permeability after exposure to certain prostaglandins is associated with increased intrascleral matrix metalloproteinases (MMPs). The present study was undertaken to determine whether these MMPs could directly alter transscleral permeability.

METHODS

Freshly enucleated mouse eyes were incubated with human MMP-1, -2, and -14 for 4 hours at 37 degrees C. The eyes then were incubated with 10 or 70 kDa dextran-tetramethylrhodamine-lysine for 16 to 32 minutes at 37 degrees C. Two methods of analysis were used. In the first, quickly isolated retinas were homogenized and centrifuged. Fluorescence in the supernatants was determined by microspectrofluorimetry. In the second, the eyes were fixed in 4% paraformaldehyde, and frozen sections were prepared. After the identity of the sections was masked, the intensity of fluorescence in anterior, middle, and posterior regions of the outer retina and inner retina was scored with a 7-point grading scheme.

RESULTS

The concentration of 10-kDa fluorescent dextran was 5.14 +/- 1.61 microg/mL (mean +/- SD, n = 33) in the control retinal supernatants, and 6.37 +/- 2.67 microg/mL (n = 40) in the retinal supernatants from the MMP-treated eyes. This increase was statistically significant (P < 0.02, t-test). The structural organization of the retina and other ocular tissues was maintained in all experimental conditions. Histologic scoring of fluorescence found significantly increased dextran in the outer retina of eyes treated with MMPs for 32 minutes (the score of control eyes was 2.5 +/- 0.4 and of MMP-treated eyes was 3.5 +/- 0.1, mean +/- SD; P = 0.02, n = 3). Analysis by region found greater scores in the third of the retina nearest to the optic nerve head.

CONCLUSIONS

These results show that MMP-1, -2, and -14 can directly increase transscleral permeability and support the view that the increased MMP-1 and -2 observed after topical PG treatment could contribute to increased uveoscleral outflow.

Magnetic resonance imaging of the visual system in vivo: Transsynaptic illumination of V1 and V2 visual cortex

Brain nuclei directly receiving retinal projections are readily labeled in magnetic resonance images following intraocular injection of manganese (Mn). To assess whether Mn in retinal ganglion cell axons can be transsynaptically delivered to visual cortex, mice that had previously received intraocular Mn injection were anesthetized with isoflurane, and T1-weighted data sets were acquired of the eyes and brain using a 7-T magnetic resonance imaging machine. Image intensity within contralateral brain structures was evaluated by assessing 1) signal-to-noise ratios, 2) mean image intensity, and 3) mean image intensity normalized to facial muscle intensity. Image intensity was increased throughout the visual pathway including within contralateral visual cortex areas V1 and V2L. Mean normalized image intensity was greater by 53% in the ipsilateral optic nerve and by 31% and 28% in the contralateral lateral geniculate nucleus and superior colliculus, respectively (N=5, P<0.02, paired t test). In contralateral visual cortex areas V1 and V2L, image intensity was increased by 7.5% and 6.8%, respectively (P<0.02 for both, paired t test). Power analysis of the different evaluation methods yielded evidence of superior sensitivity using the normalization method. Reconstruction of the visual system based upon threshold analysis allowed simultaneous visualization of all portions of the major retinal projections to the brain. These results support use of high magnetic field MRI imaging and data normalization for in vivo quantitative analysis of the mouse brain visual system including visual cortex.

Comparison of invasive and non-invasive tonometry in the mouse

Assessment of the accuracy of non-invasive rebound tonometry, and comparison with invasive cannulation tonometry. An in vivo calibration technique was devised to improve the accuracy of the rebound tonometer. IOP was then measured in SW mice using both rebound and cannulation tonometry. The ability of the rebound tonometer to accurately measure small IOP reductions after instillation of a topical prostaglandin was also determined. With the rebound method, mid-afternoon IOP in two groups of similar aged SW mice was 15.9+/-3.9 mmHg (mean+/-s.d., n=25) compared to 16.3+/-1.2 mmHg (n=32) using the cannulation technique. This difference was not statistically significant (p=0.6). For serial measurements using both techniques in the same eyes of a third group of SW mice (n=14), mean IOP was 15.0+/-3.9 mmHg for rebound tonometry but only 13.4+/-2.3 mmHg for subsequent cannulation tonometry. This effect was subsequently shown to be a consequence of the rebound tonometry, as multiple rebound measurements induced a statistically significant reduction in IOP. The average IOP reduction observed 2 hr after a single application of topical latanoprost (200 ng) was 2.8+/-1.3 mmHg (p<0.001) and 2.4+/-4.7 mmHg (p=0.03) with cannulation and rebound tonometers, respectively. These differences were not significantly different (p=0.8). In vivo calibration of the rebound tonometer increased measurement accuracy and provided IOP values within the physiological range that agreed closely with the IOP measured by cannulation tonometry. However, IOP measurement with the rebound tonometer had larger variability compared with the cannulation method. Repeat IOP measurements with the rebound tonometer led to a reduction in IOP. The rebound tonometer was sufficiently sensitive to detect a 2-3 mmHg reduction in IOP following application of topical latanoprost. Despite these limitations, the rebound tonometer has a significant advantage over cannulation tonometry in that it permits longitudinal IOP measurement in conscious mice.

Effect of Bimatoprost on Intraocular Pressure in Prostaglandin FP Receptor Knockout Mice

PURPOSE

To determine the effect of bimatoprost on intraocular pressure in the prostaglandin FP receptor knockout mouse.

METHODS

The IOP response to a single 1.2-microg (4 microL) dose of bimatoprost was measured in the treated and untreated fellow eyes of homozygote (FP+/+, n = 9) and heterozygote (FP+/-, n = 10) FP-knockout mice, as well as in wild-type C57BL/6 mice (FP+/+, n = 20). Serial IOP measurements were also performed after topical bimatoprost in a separate generation of homozygous FP-knockout mice and wild-type littermate control animals (n = 4 per group). Aqueous humor protein concentrations were measured to establish the state of the blood-aqueous barrier. Tissue, aqueous humor and vitreous concentrations of bimatoprost, latanoprost, and their C-1 free acids were determined by liquid chromatography and tandem mass spectrometry.

RESULTS

A significant reduction in IOP was observed in the bimatoprost-treated eye of wild-type mice at 2 hours, with a mean difference and 95% confidence interval (CI) of the difference in means of -1.33 mm Hg (-0.81 to -1.84). Bimatoprost did not lead to a significant reduction in IOP in either the heterozygous knockout -0.36 mm Hg (-0.82 to +0.09) or homozygous FP-knockout mice 0.25 mm Hg (-0.38 to +0.89). The lack of an IOP response in the FP-knockout mice was not a consequence of blood-aqueous barrier breakdown, as there was no significant difference in aqueous humor protein concentration between treated and fellow eyes. Tissue and aqueous humor concentrations of bimatoprost, latanoprost, and their C-1 free acids indicate that latanoprost, but not bimatoprost, is hydrolyzed in the mouse eye after topical administration.

CONCLUSIONS

An intact FP receptor gene is critical to the IOP response to bimatoprost in the mouse eye.

The importance of models in glaucoma research

Experimental models have enhanced our understanding of the biology of glaucoma. Moreover, they have enabled the testing of potential therapies prior to the initiation of human trials. Each have advantages and limitations. In vitro cell and organ culture offer direct cellular accessibility and microenvironmental control, as well as efficient comparison between many experimental conditions or potential therapeutic compounds. However, they generally have less relevance to clinical glaucoma than in vivo models. Rat models allow moderate sized investigations of intact biological systems that have greater relevance to glaucoma than in vitro experiments, but less than primate experiments. Mouse models are similar to rat models but have the advantage of investigating mutant and transgenic strains mimicking specific aspects of glaucoma that are not available in other model systems. Primate models of glaucoma generally are the most relevant to human glaucoma but must be limited in scope because of availability and the high cost of experimentation.

Elevated Intraocular Pressure and Transgenic Applications in the Mouse

Exploitation of the mouse as a model for glaucoma has been advanced by the development of methods to measure mouse intraocular pressure (IOP), identification of mutant mouse strains in which IOP spontaneously increases, and the development of treatments to induce elevated IOP. These developments enable investigations that directly test the influence of specific gene product alterations on the progression of glaucoma. Moreover, new transgenic mouse models have been produced with genetic mutations that parallel human gene mutations that have been linked to the onset of glaucoma. These new mouse models and technologies have potential for uncovering the biological basis of glaucoma as well as for evaluating new treatments.

Regional optic nerve damage in experimental mouse glaucoma

PURPOSE

To assess the relationship between regional variation of axon loss and optic nerve head anatomy in laser-induced experimental glaucoma in the mouse.

METHODS

Experimental glaucoma was induced unilaterally in eight NIH Swiss black mice. Intraocular pressure (IOP) was measured for 12 weeks, and the mice were killed. The eyes were enucleated, and both optic nerves were dissected and processed conventionally for electron microscopy. Low- and high-magnification images of the optic nerve cross sections 300 microm posterior to the globe were collected systematically and masked before analysis. For each nerve, cross-sectional area was measured in low-magnification micrographs. Axon number and density were determined in the high-magnification micrographs. Loss of axonal density was compared between the superior and inferior and nasal and temporal areas of the optic nerve cross section. Additional cross-section micrographs were collected at 10- or 20-microm intervals throughout the optic nerve head.

RESULTS

In the treated (glaucoma) eyes, mean IOP was 44% higher than that in the control eyes. The optic nerve cross-sectional area, mean axonal density, and total axonal number were significantly less than those in the control eyes (P < 0.01 for each). Axon loss in the superior optic nerve was greater than in the inferior optic nerve in each glaucomatous eye (P = 0.012). The ratio of axonal density in the superior and inferior optic nerve (superior-to-inferior [S/I] ratio) in all treated eyes was <1.0 and significantly lower than that in the control eyes (P = 0.012). The central retinal vessels occupied approximately 20% of the central optic nerve head cross-sectional area, gradually shifted position ventrally as they progressed toward the scleral foramen (the mouse does not have a lamina cribrosa), and exited the inferior retrobulbar optic nerve adjacent to the posterior of the globe.

CONCLUSIONS

Ocular hypertension in the mouse eye sufficient to cause optic nerve damage induces preferential loss of superior optic nerve axons. Optic nerve axon loss appeared less among the axons that were near the major optic nerve blood vessels at the scleral foramen. Topographic differences in optic nerve axon loss should be considered when evaluating optic nerve damage in experimental laser-induced glaucoma in the mouse.

Prostaglandin FP Agonists Alter Metalloproteinase Gene Expression in Sclera

PURPOSE

The present study was undertaken to determine whether exposure of the sclera to prostaglandin (PG)F(2alpha) or to the PGF(2alpha) analogue latanoprost acid alters mRNA for matrix metalloproteinases.

METHOD

Fifteen human eye bank eyes were studied. Circular pieces of sclera were either immediately preserved in a stabilization reagent or cultured in low-serum DMEM/F-12 medium. The cultures were treated for 24 hours with medium supplemented with PGF(2a), latanoprost acid, or vehicle. Total RNA was then isolated, and the expression of mRNA for matrix metalloproteinase (MMP)-1, -2, -3, -8, -9, -10, and -12 were determined by real-time PCR. All results were normalized according to the GAPDH mRNA in each sample. Altered mRNA expression after PG treatments also was evaluated with microarrays containing 19 MMP genes and 4 tissue inhibitor of matrix metalloproteinase (TIMP) genes.

RESULTS

Real-time PCR results showed that 24 hours of exposure to 100 nM PGF(2alpha) significantly increased mRNA for MMP-1 and -9 (P < 0.06 Wilcoxon test) and that exposure to 100 nM latanoprost acid significantly increased mRNA for MMP-9 (P < 0.06 Wilcoxon test). Array analysis demonstrated increases of MMP-3 and -10 mRNA after exposure to 100 nM latanoprost and further increases after exposure to 200 nM latanoprost. The array results also showed that latanoprost induced dose-dependent increases in the expression of TIMP-1, -2, and -3 mRNA in the scleral cultures.

CONCLUSIONS

PGF(2alpha) and latanoprost acid induce coordinated alterations of MMP gene transcription in scleral organ cultures. These results indicate that PGs can directly trigger MMP gene transcription changes within the sclera. These changes support a role for increased MMPs in the enhancement of uveoscleral outflow that occurs after topical treatment with latanoprost.

Effect of Latanoprost on Intraocular Pressure in Mice Lacking the Prostaglandin FP Receptor

PURPOSE

To determine whether latanoprost lowers IOP in prostaglandin FP receptor knockout mice.

METHODS

Mean IOP difference between treated and untreated fellow eyes was measured on three separate occasions, 2 hours after a 200-ng dose of latanoprost to the right eye of homozygous (n = 9) and heterozygous (n = 15) FP knockout mice. C57BL/6 (n = 10) and NIH Swiss white mice (n = 17), which have normal FP receptor expression, provided the control population. The investigator was masked to the genotype of the FP knockout mice at the time of IOP measurement.

RESULTS

Latanoprost had no effect on IOP in the homozygous FP knockout mice, with an average difference in IOP between treated and untreated fellow eyes of +0.25 mm Hg and a 95% confidence interval (CI) for the difference between means of -0.019 to +0.69. In contrast, latanoprost reduced IOP in the treated eye of the heterozygous FP knockout, C57BL/6, and Swiss white mice with mean differences and 95% CI of the difference in means of -0.52 (-0.91 to -0.14), -1.38 (-2.1 to -0.70), and -1.29 (-1.78 to -0.79) mm Hg, respectively.

CONCLUSIONS

FP receptor signaling plays a crucial role in the early IOP response to latanoprost in the mouse eye.

Optic nerve damage in mice with a targeted type I collagen mutation

PURPOSE

Transgenic (Col1a1(r/r)) mice gradually develop elevated intraocular pressure (IOP) with open angles. The present study was undertaken to evaluate optic nerve axonal loss with time in these mice.

METHODS

The IOP of transgenic (Col1a1(r/r)) mice and control wild-type (Col1a1(+/+)) mice was measured at 7, 12, 16, 24, 36, and 54 weeks of age using a microneedle method. Transgenic Col1a1(r/r) and control Col1a1(+/+) mice at 24 and 54 weeks of age were randomly selected and their optic nerves were processed conventionally for electron microscopy. Optic nerve cross-sections were collected 300 micro m posterior to the globe. Low (200X) and high (10,000X) magnification images were collected systematically and were masked before analysis. For each nerve, cross-sectional area was measured in low magnification images, and axonal number was counted in high magnification images.

RESULTS

Mean IOP of the transgenic Col1a1(r/r) mice was significantly higher than that of the control Col1a1(+/+) mice at 16, 24, 36, and 54 weeks by 21%, 42%, 41%, and 33% respectively (P < 0.05). The mean axonal density and total axonal number in the transgenic Col1a1(r/r) mice at 54 weeks of age (n = 10) was significantly less than those in the control Col1a1(+/+) mice at 24 weeks (n = 5) and 54 weeks (n = 5; P = 0.0081 and P = 0.020, respectively, analysis of variance, P < 0.05 for pair-wise comparisons). The mean axonal density and total axonal number in the transgenic Col1a1(r/r) mice at 54 weeks also were significantly less than in the transgenic Col1a1(r/r) mice at 24 weeks (n = 10). Mean axonal loss between 24 and 54 weeks of age in the transgenic Col1a1(r/r) mice was 28.7%.

CONCLUSIONS

Transgenic Col1a1(r/r) mice develop sustained elevation of IOP and progressive optic nerve axon loss. This suggests that these mice may be useful as a mouse model of primary open angle glaucoma as well as for assessing the relationship between collagen type I metabolism and optic nerve axon loss.

Effect of Latanoprost on Outflow Facility in the Mouse

PURPOSE

To assess the early effect of latanoprost on outflow facility and aqueous humor dynamics in the mouse.

METHODS

Aqueous humor dynamics in NIH Swiss White mice were assessed with an injection and aspiration system, using fine glass microneedles. A single 200-ng (4 microL) dose of latanoprost was applied to one eye 2 hours before measurement. The fellow eye served as a control. Intraocular pressure (IOP) was measured by using an established microneedle procedure. Outflow facility (C) was determined by constant-pressure perfusion measurements obtained at two different IOPs. Aqueous humor flow (Fa) was determined by a dilution method using rhodamine-dextran. Conventional and uveoscleral outflow (Fc and Fu) were calculated by the Goldmann equation.

RESULTS

Average IOP, Fa, and C of control eyes were 15.7 +/- 1.0 mm Hg, 0.144 +/- 0.04 microL/min (mean +/- SD, n = 8), and 0.0053 +/- 0.0014 microL/min per mm Hg (n = 21), respectively. Average IOP, Fa, and C of treated eyes were 14.0 +/- 0.8 mm Hg, 0.138 +/- 0.04 microL/min (n = 8 for each), and 0.0074 +/- 0.0016 microL/min per mm Hg (n = 21), respectively. The differences between treated and control eyes were significant for IOP and total outflow facility only.

CONCLUSIONS

These data indicate that the early hypotensive effect of latanoprost in the mouse eye is associated with a significant increase in total outflow facility. Alterations in the aqueous dynamics induced by latanoprost can be measured reproducibly in the mouse and may provide a useful model for further determining the mechanism by which latanoprost reduces IOP and alters outflow facility.

β-Catenin regulates the gene of MMP-26, a novel matrix metalloproteinase expressed both in carcinomas and normal epithelial cells

There are several unorthodox features, which distinguish the non-redundant and unique novel matrix metalloproteinase-26 (MMP-26) (an enzyme that has recently evolved and does not exist in rodents but is present in humans) from other members of the MMP superfamily. This report describes our recent efforts to gain a better understanding of the mechanisms which restrict expression of MMP-26 to certain cell/tissue types. We examined transcriptional regulation of the human MMP-26 gene in normal and malignant cells. The AP-1 and Tcf-4 sites of the MMP-26 promoter appear most potent in regulating the expression of the MMP-26-luciferase chimera in HEK293 embryonic kidney and MCF7 breast carcinoma cells. Key regulators of the Wnt pathway (beta-catenin and lymphoid enhancer-binding factor/T-cell factor with which beta-catenin associates) enhanced the transcriptional activity of MMP-26 suggesting that the MMP-26 gene is a likely target of the Wnt pathway. Immunostaining, gene arrays and reverse-transcriptase polymerase chain reaction (RT-PCR) confirm the presence of MMP-26 in normal cells, including the apical epithelial conjunctiva cells of the human eye, as well as in malignant cells of epithelial origin. MMP-26 predominantly accumulates in its proenzyme form in the intracellular milieu of the transfected breast carcinoma MCF7 cells. This study brings us a step forward towards a better understanding of the unconventional role, regulation and functions of epithelial cell MMP-26 in physiological conditions and in neoplasms.

Influence of molecular weight on intracameral dextran movement to the posterior segment of the mouse eye

PURPOSE

Uveoscleral outflow provides a potential pathway to the posterior segment for drug delivery. In this study, the influence of molecular weight on the intraocular distribution of dextran molecules after intracameral injection in the mouse eye was investigated.

METHODS

The anterior chambers of the eyes of 64 anesthetized NIH Swiss mice were perfused with various fluorescent dextran solutions (10, 40, 70, and 500 kDa) at 500 nL/min for 10 minutes. At 10, 20, or 60 minutes after the initiation of the anterior chamber perfusion, the mice were killed and tissue obtained for evaluation by fluorescence microscopy.

RESULTS

Each of the different molecular weight dextrans were visible in the anterior chamber of the mouse eye after the termination of the experiments. The 10-kDa dextran was observed in the supraciliary space and the supraciliary sclera after 10 minutes and in the anterior sclera after 60 minutes of perfusion. The 40-kDa dextran was detected in the supraciliary space and the anterior sclera after 10 minutes and in the anterior choroid and sclera after 20 and 60 minutes, but not in the posterior segment. The 70-kDa dextran was observed in the supraciliary space and anterior choroid after 10 minutes. After 20 minutes, it was visible in the equatorial choroid. After 60 minutes, it was observed in the posterior choroid. The 500-kDa dextran was observed in the supraciliary space and the anterior choroid after 10 minutes and in the supraciliary sclera at 20 minutes. At 60 minutes, 500-kDa dextran was observed in the equatorial choroid, but not farther toward the posterior.

CONCLUSIONS

The influence of molecular weight on the redistribution of macromolecules from the anterior chamber to the posterior globe in the mouse eye appears to be similar to primate eyes. These similarities include passage of all size dextrans through the proximal uveoscleral pathway, the dependence of the extent of posterior movement on the size of the dextran, and the absence of large dextran entry into the distal uveoscleral pathway.

Twenty-four-hour pattern of mouse intraocular pressure

The 24-hr pattern of intraocular pressure in the mouse eye remains poorly characterized. The present study was undertaken to determine the magnitude, dynamic pattern, and synchrony of the 24-hr pattern of intraocular pressure (IOP) in NIH Swiss mice exposed to a 12-hr light/dark cycle or to constant light. IOP was measured every 3 hr using a microneedle method. Mice exposed to a 12-hr light /dark cycle were either measured repeatedly at 1 week interval (group 1) or were only measured once (group 2). A third group was exposed to constant light for 2 weeks prior to IOP measurements. The 24-hr IOP pattern in the first and second groups showed a similar rhythmic pattern that appeared to be sinusoidal. This IOP pattern declined in the morning until 12:00, and then increased in the early evening until 21:00. In contrast, IOP in the third group was asynchronous with some mice exhibiting multiple peaks and troughs during the 24-hr period. These results show that 24-hr IOP pattern in mouse eyes is biphasic and that extended exposure to constant light disrupts this 24-hr IOP pattern.

Aqueous Humor Dynamics in Mice

PURPOSE

To assess aqueous humor dynamics in mouse eyes.

METHODS

Aqueous humor dynamics of NIH Swiss White mouse were assessed with an injection and aspiration system, using fine glass microneedles. Intraocular pressure (IOP) was measured by a microneedle connected to a pressure transducer. Episcleral venous pressure (EVP) was measured by gradually lowering intracameral pressure until blood reflux into Schlemm's canal was observed. Outflow facility (C) was determined based on constant pressure perfusion measurements obtained at two different IOPs. Aqueous volume (V(a)) was determined by direct measurement of aspirated aqueous humor. Aqueous humor production (F(a)) was measured by the dilution method with rhodamine-dextran. Conventional and uveoscleral outflow (F(c) and F(u), respectively), as well as the turnover rate of aqueous humor, were also calculated.

RESULTS

IOP and EVP were 15.7 +/- 2.0 and 9.5 +/- 1.2 mm Hg, respectively (n = 20). F(a) was 0.18 +/- 0.05 microL/min (mean +/- SD; n = 8). C was 0.0051 +/- 0.0006 microL/min per mm Hg (n = 8). Estimated F(c) and F(u) were 0.032 and 0.148 microL/min, respectively. F(c) was 18% of F(a). F(u) was 82% of F(a). V(a) was 5.9 +/- 0.5 microL (n = 8). The calculated turnover rate of aqueous humor was 2.5%.

CONCLUSIONS

The mouse eye has similar aqueous production and aqueous humor turnover rate as the human eye. The presence of both conventional and uveoscleral outflow suggests that the mouse is a useful model system for further investigations of the biology of aqueous dynamics.

Experimental mouse ocular hypertension: establishment of the model

PURPOSE

To establish an experimental model of ocular hypertension in the mouse.

METHODS

Twenty-two black Swiss mice were used. After anesthesia and pupil dilation, the anterior chamber was flattened by the aspiration of aqueous humor. Laser photocoagulation (532-nm wavelength, 200-mW power, 0.05-second duration, 200- micro m spot size) then was performed at the limbus. Intraocular pressure (IOP) was measured weekly for 4 weeks and biweekly for 12 weeks, by a microneedle method. Slit lamp biomicroscopy was performed throughout the period and the structural changes were assessed histologically. A treatment response was considered to be a success if either the mean of IOP measurements collected during the first 4 weeks was increased by 30% or more, or the mean of all measurements collected during the 12 week study period was increased by 30% or more.

RESULTS

Laser-treated eyes showed significantly higher IOP than control eyes from 1 to 6 weeks (P < 0.001). The average IOP in treated eyes during the first 4 and 12 weeks was significantly higher than the control IOP (P < 0.001). These IOP increases were 7.1 and 3.8 mm Hg, respectively. During the first 4 weeks, sustained elevation of IOP was obtained in 64% (14/22) of the treated eyes. During the entire 12-week study, increased IOP was successfully maintained in 37% (7/19) of the treated eyes. After 6 weeks, elevated IOP often returned to normal or several mm Hg below normal. Histologic analysis at the end of the 12-week study showed no inflammatory cells in the anterior segment and confirmed that the angle was closed by the laser photocoagulation treatment.

CONCLUSIONS

This method produces persistent IOP elevation in mouse eyes and may be a promising experimental model for the investigation of the biological mechanisms of glaucomatous optic neuropathy.

Optic Nerve Damage in Experimental Mouse Ocular Hypertension

PURPOSE

To evaluate optic nerve damage in mice after laser-induced ocular hypertension.

METHODS

Ocular hypertension was induced unilaterally in 13 NIH Black Swiss mice by laser photocoagulation of the limbus. Over the following 12 weeks, intraocular pressure (IOP) was measured at regular intervals by the microneedle method. The optic nerves of these mice and of seven normal untreated mice were then processed conventionally for electron microscopy, and cross sections of the nerve 300 micro m posterior to the globe were collected. Low- and high-magnification images were collected systematically and masked before analysis. For each nerve, cross-sectional area was measured in low-magnification micrographs, and axon and glia numbers were counted in high-magnification micrographs.

RESULTS

In normal untreated mice, the average number of axons was 59,597 +/- 3,112 (mean +/- SD). Variation among these measurements was 5.7% +/- 3.9%. After laser treatment, the duration of high IOP ranged from 2 to 12 weeks (6.2 +/- 3.6 weeks, mean +/- SD). The mean IOP in the treated eyes was 1.3 times greater than the mean IOP in the control eyes (P = 0.0012). The maximum IOP in the treated eyes was 1.6 times greater than that observed in the control eyes (P < 0.0001). The optic nerve cross-sectional area, mean axon density, and total number of axons in the treated eyes were significantly less than in the control eyes (28.5% +/- 23.4%, 57.8% +/- 37.8%, and 63.1% +/- 38.1%, respectively; P < 0.005 for each). The decrease in optic nerve cross-sectional area and the positive integral of elevated IOP and duration of IOP elevation correlated significantly with total axon loss (r(2) = 0.79, P < 0.0001 and r(2) = 0.36, P = 0.040, respectively). The number of astrocytes per cross section of optic nerve was significantly greater in the treated eyes than in the control eyes (P = 0.014).

CONCLUSIONS

Laser-induced ocular hypertension in mouse eyes can induce optic nerve axon loss that correlates with the magnitude and duration of elevated IOP.

Ocular hypertension in mice with a targeted type I collagen mutation

PURPOSE

To evaluate intraocular pressure (IOP) in transgenic mice with a targeted mutation in the gene for the alpha1 subunit of collagen type I.

METHODS

Homozygous B6; 129-Cola1(tm1Jae) mice and corresponding wild-type mice were anesthetized. A fluid-filled glass microneedle connected to a pressure transducer was then inserted through the cornea into the anterior chamber to measure IOP. All measurements were made between 11:30 AM and 1:30 PM. The IOP of seven Col1a1(r/r) and eight corresponding wild-type Col1a1(+/+) male mice was measured at 12, 18, 24, and 36 weeks after birth. The IOP of 5 to 24 additional Col1a1(r/r) mice was measured at 7, 12, 18, 24, and 36 weeks after birth. The structure of the anterior segment and the distribution of collagen I were assessed by immunohistochemistry.

RESULTS

Mean IOP measurements of the control Col1a1(+/+) mice (IOP(c)) at 12 and 18 weeks after birth were relatively constant at 18.9 +/- 2.0 and 19.2 +/- 1.9 mm Hg, respectively. Mean IOP then decreased to 15.8 +/- 0.8 and 16.2 +/- 1.2 mm Hg at 24 and 36 weeks, respectively. In contrast, mean IOP measurements in the transgenic (Col1a1(r/r)) mice was 2.7 +/- 3.4 mm Hg higher at 12 weeks and increased to a maximum of 23.6 +/- 2.4 mm Hg at 24 weeks. The difference between mean IOP in these two groups gradually increased to a maximum of 4.8 mm Hg (30%) at 36 weeks and was significantly different from the control mice at both 24 and 36 weeks of age. No anterior segment abnormality was observed in Col1a1(r/r) mice and no difference between the anterior segment appearance of Col1a1(r/r) and Col1a1(+/+) mice was observed throughout the 36-week analysis period. However, collagen I immunoreactivity in sclera and associated structures was greater in Col1a1(r/r) mice than in Col1a1(+/+) mice. When the mean IOP measurements from the additional Col1a1(r/r) mice were included with these measurements, mean IOP at each age was 16.7 +/- 0.8, 21.8 +/- 3.9, 23.2 +/- 2.8, 23.5 +/- 2.4, and 22.1 +/- 3.6 mm Hg, respectively. Mean IOP in the Col1a1(r/r) mice was significantly higher than in the Col1a1(+/+) mice at 18, 24, and 36 weeks by 21%, 44%, and 36%, respectively (P < 0.05).

CONCLUSIONS

These results demonstrate ocular hypertension in mice with a targeted type I collagen mutation and suggest there is an association between IOP regulation and fibrillar collagen turnover.

Latanoprost's effects on TIMP-1 and TIMP-2 expression in human ciliary muscle cells

PURPOSE

To determine the effect of treatment with latanoprost on the tissue inhibitors of metalloproteinase (TIMP)-1 and -2 in cultured human ciliary muscle (HCM) cells.

METHODS

Confluent serum-starved HCM cells were exposed to increasing concentrations of latanoprost acid (LA, 1 nM to 10 micro M) for 6, 18, and 24 hours. TIMP-1 and -2 mRNA transcripts were evaluated by RT-PCR. Gelatin zymography was used to measure changes in the amount of matrix metalloproteinase (MMP) in the culture medium. To evaluate the potential role of PKC, HCM cells were treated with phorbol 12-myrisate 13-acetate (PMA) in the absence or presence of the PKC inhibitor bisindolylmaleimide I (Bis I) or the PKA inhibitor KT5720. Data were quantitated by densitometry and statistically analyzed with the Student-Newman-Keuls test.

RESULTS

TIMP-1 and -2 mRNA transcripts and proteins were detected in primary cultures of HCM cells. TIMP-1 mRNA levels were unchanged at 6 hours, but increased 45% +/- 17% and 54% +/- 13% in cultures exposed for 18 hours to 1 and 10 micro M LA, respectively (n = 3). In contrast, 6 hours of exposure to LA increased expression of TIMP-2 mRNA by up to 11.3% +/- 0.2% (n = 3). However, no significant induction of TIMP-2 mRNA was observed at either 18 or 24 hours (n = 3). TIMP-1 protein was significantly increased in cultures exposed to LA for 18 and 24 hours. In contrast, TIMP-2 protein expression was insignificantly different from control cultures at 6, 18, and 24 hours of treatment. HCM cells exposed to PMA for 24 hours produced similar increases in TIMP-1 mRNA levels, as seen with latanoprost (n = 5). However, no significant induction of TIMP-2 mRNA was observed. Zymographic analysis of the media from these cultures confirmed dose-dependent increases of MMP-1 at 6, 18, and 24 hours, whereas dose-dependent increases in MMP-2 were seen only after 24 hours' exposure to LA (n = 3). TIMP-1 protein levels were increased 27% +/- 9.3% and 15% +/- 11% in the media of cells exposed for 24 hours to 100 nM LA and 100 nM PMA, respectively (n = 5). The increases in TIMP-1 protein induced by LA were essentially eliminated by Bis I (n = 3) and unaffected by KT5720 (n = 3).

CONCLUSIONS

For the most part, TIMP-1, and not TIMP-2, contributes to regulation of MMP within the uveoscleral outflow pathway after exposure to latanoprost. Moreover, this induction appears to be meditated by activation of PKC.

Effects of prostaglandins on the aqueous humor outflow pathways

Topical treatments with certain prostaglandins (PGs), including FP receptor agonists, lower intraocular pressure by increasing uveoscleral outflow. Although the precise mechanism for the increased uveoscleral outflow is not known, there appears to be activation of a molecular transduction cascade and an increase in the biosynthesis of certain metalloproteinases. This leads to reduction of extracellular matrix components within the ciliary muscle, iris root, and sclera. It is possible that this reduction of extracellular matrix present within portions of the uveoscleral pathway may contribute to the mechanism of increased uveoscleral outflow. Additional mechanisms that may contribute to the PG-mediated increase of uveoscleral outflow include relaxation of the ciliary muscle, cell shape changes, cytoskeletal alteration, or compaction of the extracellular matrix within the tissues of the uveoscleral outflow pathway. Future studies should clarify the importance of these various responses that may contribute to increased uveoscleral outflow. At present, there is no compelling evidence for a substantial facility-increasing effect on the trabecular meshwork outflow for any of these compounds.

Identification of the mouse uveoscleral outflow pathway using fluorescent dextran

PURPOSE

This study was undertaken to assess directly whether there is uveoscleral outflow in the mouse eye by monitoring the movement of intracamerally injected fluorescent dextran.

METHODS

After anesthesia, NIH Swiss mice received intracameral injection of 1.5 microL of 0.2 pg/microL 70-kDa dextran conjugated to tetramethyl-rhodamine and to lysine. After survival times of 10, 20, 60, and 120 minutes, the experiments were terminated by transcardial perfusion with 2% paraformaldehyde. The eyes were enucleated and embedded in paraffin, and sections were prepared. These sections were then analyzed by fluorescence microscopy.

RESULTS

Fluorescent tracer in the eyes of animals that survived for 10 minutes was prominent in the iris root and ciliary processes and was of moderate intensity in the adjacent sclera. Moderate intensity fluorescence also was observed in the trabecular meshwork and adjacent cornea. At 20 minutes, intense fluorescence was observed in the ciliary processes and the ciliary muscle. This fluorescence in the ciliary muscle extended from the posterior edge of the ciliary muscle's tail into the anterior choroid. At 60 minutes, the fluorescence in the choroid extended to the equator and adjacent sclera. The intensity of the fluorescence within the ciliary processes of these eyes was substantially reduced when compared with the 20-minute-survival eyes. At 120 minutes, label was observed only within trabecular meshwork and Schlemm's canal.

CONCLUSIONS

These results indicate that at least a portion of aqueous outflow in the mouse eye is through the uveoscleral outflow pathway.

Intraocular distribution of 70-kDa dextran after subconjunctival injection in mice

PURPOSE

To investigate the intraocular distribution kinetics of 70-kDa dextran after subconjunctival injection.

METHODS

The right eye of 15 mice received a single subconjunctival injection of a 1.5-microL solution of 0.25% 70-kDa tetramethylrhodamine-dextran (TMR-D). The distribution of fluorescent labeling in eye sections was examined by fluorescence microscopy at 0.25, 1, 4, 24, or 72 hours after the injection. The brightness and homogeneity of fluorescence in the sclera, choroid, and retina were scored near the injection site, on the side of the globe opposite the injection site, and adjacent to the optic nerve head. Fluorescence intensity within the sclera and choroid adjacent to the optic nerve was assessed quantitatively by imaging densitometry.

RESULTS

TMR-D readily diffused transsclerally and dispersed throughout a large portion of the sclera, uvea, and cornea. Shortly after the injection, homogenous fluorescence was observed in the sclera and choroid on the same meridian as that of the injection site. This fluorescence gradually decreased in intensity with distance from the injection site. At the opposite meridian, fluorescence in the choroid was more intense than in the adjacent sclera and could be traced up to the ciliary muscle. TMR-D was also observed in the retinal and optic nerve vessels. The intensity of scleral and choroidal fluorescence adjacent to the optic nerve reached a maxima at 1 hour, and then decreased slowly, with half-lives of approximately 16 and 100 hours, respectively. Visible fluorescence was maintained at least until 72 hours in the sclera, choroid, iris, and cornea. Specific fluorescent labeling was never found in the contralateral eyes.

CONCLUSIONS

Macromolecular 70-kDa dextran can be readily delivered to the mouse retina and uveal tissues by subconjunctival injection through transscleral diffusion, local hematogenous spread, and possibly movement through the uveoscleral outflow pathway. Subconjunctival injection may be a useful approach for delivering macromolecules to the retina and uvea.