Dr. Crosson is Professor in the Department of Ophthalmology at the Medical University of South Carolina (MUSC). He is also Director of the Ola B. Williams Glaucoma Therapeutic Development Center and Senior Associate Dean for Research at MUSC. His research interests include ischemia, neovascularization, and neuroprotection. Current research in his laboratory is targeting pharmacological treatment for elevated intraocular pressure, retinal degenerations and macular edema.
Suppression of Acid Sphingomyelinase Protects the Retina from Ischemic Injury.
Invest Ophthalmol Vis Sci. 2016 Aug 1;57(10):4476-84
Authors: Fan J, Wu BX, Crosson CE
PURPOSE: Acid sphingomyelinase (ASMase) catalyzes the hydrolysis of sphingomyelin to ceramide and mediates multiple responses involved in inflammatory and apoptotic signaling. However, the role ASMase plays in ischemic retinal injury has not been investigated. The purpose of this study was to investigate how reduced ASMase expression impacts retinal ischemic injury.
METHODS: Changes in ceramide levels and ASMase activity were determined by high performance liquid chromatography-tandem mass spectrometry analysis and ASMase activity. Retinal function and morphology were assessed by electroretinography (ERG) and morphometric analyses. Levels of TNF-α were determined by ELISA. Activation of p38 MAP kinase was assessed by Western blot analysis.
RESULTS: In wild-type mice, ischemia produced a significant increase in retinal ASMase activity and ceramide levels. These increases were associated with functional deficits as measured by ERG analysis and significant structural degeneration in most retinal layers. In ASMase+/- mice, retinal ischemia did not significantly alter ASMase activity, and the rise in ceramide levels were significantly reduced compared to levels in retinas from wild-type mice. In ASMase+/- mice, functional and morphometric analyses of ischemic eyes revealed significantly less retinal degeneration than in injured retinas from wild-type mice. The ischemia-induced increase in retinal TNF-α levels was suppressed by the administration of the ASMase inhibitor desipramine, or by reducing ASMase expression.
CONCLUSIONS: Our results demonstrate that reducing ASMase expression provides partial protection from ischemic injury. Hence, the production of ceramide and subsequent mediators plays a role in the development of ischemic retinal injury. Modulating ASMase may present new opportunities for adjunctive therapies when treating retinal ischemic disorders.
PMID: 27571014 [PubMed - in process]
Progressive Early Breakdown of Retinal Pigment Epithelium Function in Hyperglycemic Rats.
Invest Ophthalmol Vis Sci. 2016 May 1;57(6):2706-13
Authors: Desjardins DM, Yates PW, Dahrouj M, Liu Y, Crosson CE, Ablonczy Z
PURPOSE: Diabetic macular edema (DME), an accumulation of fluid in the subretinal space, is a significant cause of vision loss. The impact of diabetes on the breakdown of the inner blood-retina barrier (BRB) is an established event that leads to DME. However, the role of the outer BRB in ocular diabetes has received limited attention. We present evidence that the breakdown of normal RPE function in hyperglycemia facilitates conditions conducive to DME pathogenesis.
METHODS: Brown Norway rats (130-150 g) were injected intraperitoneally with streptozotocin (STZ; 60 mg/kg) to induce hyperglycemia. After 4 weeks, Evans blue (EB) dye was injected intravenously to determine whether there was leakage of albumin into the retina. Subretinal saline blebs (0.5-1 μL) were placed 4 and 9 weeks after STZ injection, and time-lapse optical coherence tomography tracked the resorption rate. In a subset of rats, intravitreal bevacizumab, a humanized monoclonal antibody targeted to VEGF, was given at 5 weeks and resorption was measured at 9 weeks.
RESULTS: The ability of the RPE to transport fluid was reduced significantly after 4 and 9 weeks of hyperglycemia with a reduction of over 67% at 9 weeks. No EB dye leakage from inner retinal vessels was measured in hyperglycemic animals compared to control. The intravitreal administration of bevacizumab at week 5 significantly increased the rate of fluid transport in rats subjected to hyperglycemia for 9 weeks.
CONCLUSIONS: These results demonstrate that chronic hyperglycemia altered RPE fluid transport, in part dependent on the actions of VEGF. These results support the idea that RPE dysfunction is an early event associated with hyperglycemia that contributes to fluid accumulation in DME.
PMID: 27191823 [PubMed - in process]
Histone Deacetylase Inhibition Restores Retinal Pigment Epithelium Function in Hyperglycemia.
PLoS One. 2016;11(9):e0162596
Authors: Desjardins D, Liu Y, Crosson CE, Ablonczy Z
In diabetic individuals, macular edema is a major cause of vision loss. This condition is refractory to insulin therapy and has been attributed to metabolic memory. The retinal pigment epithelium (RPE) is central to maintaining fluid balance in the retina, and this function is compromised by the activation of advanced glycation end-product receptors (RAGE). Here we provide evidence that acute administration of the RAGE agonist, glycated-albumin (gAlb) or vascular endothelial growth factor (VEGF), increased histone deacetylase (HDAC) activity in RPE cells. The administration of the class I/II HDAC inhibitor, trichostatin-A (TSA), suppressed gAlb-induced reductions in RPE transepithelial resistance (in vitro) and fluid transport (in vivo). Systemic TSA also restored normal RPE fluid transport in rats with subchronic hyperglycemia. Both gAlb and VEGF increased HDAC activity and reduced acetyl-α-tubulin levels. Tubastatin-A, a relatively specific antagonist of HDAC6, inhibited gAlb-induced changes in RPE cell resistance. These data are consistent with the idea that RPE dysfunction following exposure to gAlb, VEGF, or hyperglycemia is associated with increased HDAC6 activity and decreased acetyl-α-tubulin. Therefore, we propose inhibiting HDAC6 in the RPE as a potential therapy for preserving normal fluid homeostasis in the hyperglycemic retina.
PMID: 27617745 [PubMed - in process]
Receptor mediated disruption of retinal pigment epithelium function in acute glycated-albumin exposure.
Exp Eye Res. 2015 Jun 10;
Authors: Dahrouj M, Desjardins DM, Liu Y, Crosson CE, Ablonczy Z
Diabetic macular edema (DME) is a major cause of visual impairment. Although DME is generally believed to be a microvascular disease, dysfunction of the retinal pigment epithelium (RPE) can also contribute to its development. Advanced glycation end-products (AGE) are thought to be one of the key factors involved in the pathogenesis of diabetes in the eye, and we have previously demonstrated a rapid breakdown of RPE function following glycated-albumin (Glyc-alb, a common AGE mimetic) administration in monolayer cultures of fetal human RPE cells. Here we present new evidence that this response is attributed to apically oriented AGE receptors (RAGE). Moreover, time-lapse optical coherence tomography in Dutch-belted rabbits 48 h post intravitreal Glyc-alb injections demonstrated a significant decrease in RPE-mediated fluid resorption in vivo. In both the animal and tissue culture models, the response to Glyc-alb was blocked by the relatively selective RAGE antagonist, FPS-ZM1 and was also inhibited by ZM323881, a relatively selective vascular endothelial growth factor receptor 2 (VEGF-R2) antagonist. Our data establish that the Glyc-alb-induced breakdown of RPE function is mediated via specific RAGE and VEGF-R2 signaling both in vitro and in vivo. These results are consistent with the notion that the RPE is a key player in the pathogenesis of DME.
PMID: 26070987 [PubMed - as supplied by publisher]
Acetylation preserves retinal ganglion cell structure and function in a chronic model of ocular hypertension.
Invest Ophthalmol Vis Sci. 2014 Nov;55(11):7486-93
Authors: Alsarraf O, Fan J, Dahrouj M, Chou CJ, Yates PW, Crosson CE
PURPOSE: The current studies investigate if the histone deacetylase (HDAC) inhibitor, valproic acid (VPA), can limit retinal ganglion cell (RGC) degeneration in an ocular-hypertensive rat model.
METHODS: Intraocular pressure (IOP) was elevated unilaterally in Brown Norway rats by hypertonic saline injection. Rats received either vehicle or VPA (100 mg/kg) treatment for 28 days. Retinal ganglion cell function and number were assessed by pattern electroretinogram (pERG) and retrograde FluoroGold labeling. Western blotting and a fluorescence assay were used for determination of histone H3 acetylation and HDAC activity, respectively, at 3-day, 1-week, and 2-week time points.
RESULTS: Hypertonic saline injections increased IOPs by 7 to 14 mm Hg. In vehicle-treated animals, ocular hypertension resulted in a 29.1% and 39.4% decrease in pERG amplitudes at 2 and 4 weeks, respectively, and a 42.9% decrease in mean RGC density at 4 weeks. In comparison, VPA treatment yielded significant amplitude preservation at 2 and 4 weeks and showed significant RGC density preservation at 4 weeks. No significant difference in RGC densities or IOPs was measured between control eyes of vehicle- and VPA-treated rats. In ocular-hypertensive eyes, class I HDAC activity was significantly elevated within 1 week (13.3 ± 2.2%) and histone H3 acetylation was significantly reduced within 2 weeks following the induction of ocular hypertension.
CONCLUSIONS: Increase in HDAC activity is a relatively early retinal event induced by elevated IOP, and suppressing HDAC activity can protect RGCs from ocular-hypertensive stress. Together these data provide a basis for developing HDAC inhibitors for the treatment of optic neuropathies.
PMID: 25358731 [PubMed - indexed for MEDLINE]
Acetylation: a lysine modification with neuroprotective effects in ischemic retinal degeneration.
Exp Eye Res. 2014 Oct;127:124-31
Authors: Alsarraf O, Fan J, Dahrouj M, Chou CJ, Menick DR, Crosson CE
Neuroretinal ischemic injury contributes to several degenerative diseases in the eye and the resulting pathogenic processes involving a series of necrotic and apoptotic events. This study investigates the time and extent of changes in acetylation, and whether this influences function and survival of neuroretinal cells following injury. Studies evaluated the time course of changes in histone deacetylase (HDAC) activity, histone-H3 acetylation and caspase-3 activation levels as well as retinal morphology and function (electroretinography) following ischemia. In addition, the effect of two HDAC inhibitors, trichostatin-A and valproic acid were also investigated. In normal eyes, retinal ischemia produced a significant increase in HDAC activity within 2 h that was followed by a corresponding significant decrease in protein acetylation by 4 h. Activated caspase-3 levels were significantly elevated by 24 h. Treatment with HDAC inhibitors blocked the early decrease in protein acetylation and activation of caspase-3. Retinal immunohistochemistry demonstrated that systemic administration of trichostatin-A or valproic acid, resulted in hyperacetylation of all retinal layers after systemic treatment. In addition, HDAC inhibitors provided a significant functional and structural neuroprotection at seven days following injury relative to vehicle-treated eyes. These results provide evidence that increases in HDAC activity is an early event following retinal ischemia, and are accompanied by corresponding decreases in acetylation in advance of caspase-3 activation. In addition to preserving acetylation status, the administration of HDAC inhibitors suppressed caspase activation and provided structural and functional neuroprotection in model of ischemic retinal injury. Taken together these data provide evidence that decrease in retinal acetylation status is a central event in ischemic retinal injury, and the hyperacetylation induced by HDAC inhibition can provide acute neuroprotection.
PMID: 25064603 [PubMed - indexed for MEDLINE]
Vascular endothelial growth factor modulates the function of the retinal pigment epithelium in vivo.
Invest Ophthalmol Vis Sci. 2014 Apr;55(4):2269-75
Authors: Dahrouj M, Alsarraf O, McMillin JC, Liu Y, Crosson CE, Ablonczy Z
PURPOSE: Retinal edema, the accumulation of extracellular fluid in the retina is usually attributed to inner blood retina barrier (BRB) leakage. Vascular endothelial growth factor plays an important role in this process. The effects of VEGF on the outer BRB, the RPE, however, have received limited attention. Here, we present a methodology to assess how VEGF modulates the integrity of the RPE barrier in vivo.
METHODS: Control subretinal blebs (1-5 μL) and blebs containing VEGF (1-100 μg/mL), placental growth factor (PlGF; 100 μg/mL), or albumin (100-1000 μg/mL) were injected into New Zealand White or Dutch Belted rabbits with IOP maintained at 10, 15, or 20 mm Hg. One-hour intravitreal pretreatment with ZM323881 (10 μM/L) was used to inhibit the VEGF response. Fluid resorption was followed by optical coherence tomography for 1 hour. Retinal pigment epithelium leakage was assessed by fluorescein angiography.
RESULTS: Increasing IOP resulted in an elevated rate of bleb resorption, while increasing albumin concentration in the bleb decreased the rate of resorption. Vascular endothelial growth factor, but not PlGF, caused a significant, concentration-dependent decrease in the rate of fluid resorption, which was reversed by ZM323881. Compared with albumin-filled blebs, VEGF-filled blebs showed accelerated early-phase leakage from the choroid.
CONCLUSIONS: Consistent with a localized modulation of RPE function, VEGF induced a significant reduction in fluid resorption and an increase in hydraulic conductivity. Our results establish VEGF as a major cytokine regulating RPE barrier properties in vivo and indicate that the RPE is a principal factor in the pathogenesis of retinal edema.
PMID: 24550368 [PubMed - indexed for MEDLINE]
Pigment epithelium-derived factor decreases outflow facility.
Invest Ophthalmol Vis Sci. 2013 Oct;54(10):6655-61
Authors: Rogers ME, Navarro ID, Perkumas KM, Niere SM, Allingham RR, Crosson CE, Stamer WD
PURPOSE: Pigment epithelium-derived factor (PEDF) regulates blood-retinal barrier function. As a constituent of aqueous humor, the role of PEDF in conventional outflow function is unknown. The goals of the study were to examine the effects of PEDF on barrier function of cultured Schlemm's canal (SC) endothelia and outflow facility in mouse eyes in situ.
METHODS: To model the inner wall of SC, transendothelial electrical resistance (TEER) of human SC and porcine angular aqueous plexus (AAP) cells was monitored. To examine an intact conventional outflow pathway, enucleated eyes from culled C57BL/6 mice were perfused with PEDF using a computer-controlled system. Purified PEDF (0.1 and 1 μg/mL) was perfused at four different pressure steps (4, 8, 15, 20 mm Hg), measuring flow to determine outflow facility (slope of flow/pressure relationship).
RESULTS: Pigment epithelium-derived factor increased TEER of porcine AAP cells in a dose-dependent fashion (0.3-3 μg/mL), and 1 μg/mL recombinant PEDF or conditioned media from pigmented retinal pigment epithelial monolayers stabilized TEER of human SC monolayers over time (0-48 hours). In perfusion experiments, we observed a 43.7% decrease in outflow facility (0.016 vs. 0.029 μL/min/mm Hg, P = 4.5 × 10⁻⁵) in eyes treated with 1 μg/mL PEDF compared to vehicle-perfused controls, and a 19.9% decrease (0.021 vs. 0.027 μL/min/mm Hg, P = 0.003) at 100 ng/mL PEDF.
CONCLUSIONS: Pigment epithelium-derived factor increased barrier function in both the in vitro and in situ models of the inner wall of SC. Modification of PEDF signaling in SC cells may be therapeutically exploited to increase outflow facility in people with ocular hypertension or decrease outflow facility in those with hypotony.
PMID: 24030458 [PubMed - indexed for MEDLINE]
Inhibition of HDAC2 protects the retina from ischemic injury.
Invest Ophthalmol Vis Sci. 2013 Jun;54(6):4072-80
Authors: Fan J, Alsarraf O, Dahrouj M, Platt KA, Chou CJ, Rice DS, Crosson CE
PURPOSE: Protein acetylation is an essential mechanism in regulating transcriptional and inflammatory events. Studies have shown that nonselective histone deacetylase (HDAC) inhibitors can protect the retina from ischemic injury in rats. However, the role of specific HDAC isoforms in retinal degenerative processes remains obscure. The purpose of this study was to investigate the role of HDAC2 isoform in a mouse model of ischemic retinal injury.
METHODS: Localization of HDAC2 in mice retinas was evaluated by immunohistochemical analyses. To investigate whether selective reduction in HDAC2 activity can protect the retina from ischemic injury, Hdac2⁺/⁻ mice were utilized. Electroretinographic (ERG) and morphometric analyses were used to assess retinal function and morphology.
RESULTS: Our results demonstrated that HDAC2 is primarily localized in nuclei in inner nuclear and retinal ganglion cell layers, and HDAC2 activity accounted for approximately 35% of the total activities of HDAC1, 2, 3, and 6 in the retina. In wild-type mice, ERG a- and b-waves from ischemic eyes were significantly reduced when compared to pre-ischemia baseline values. Morphometric examination of these eyes revealed significant degeneration of inner retinal layers. In Hdac2⁺/⁻ mice, ERG a- and b-waves from ischemic eyes were significantly greater than those measured in ischemic eyes from wild-type mice. Morphologic measurements demonstrated that Hdac2⁺/⁻ mice exhibit significantly less retinal degeneration than wild-type mice.
CONCLUSIONS: This study demonstrated that suppressing HDAC2 expression can effectively reduce ischemic retinal injury. Our results support the idea that the development of selective HDAC2 inhibitors may provide an efficacious treatment for ischemic retinal injury.
PMID: 23696608 [PubMed - indexed for MEDLINE]
Essential roles of grp94 in gut homeostasis via chaperoning canonical Wnt pathway.
Proc Natl Acad Sci U S A. 2013 Apr 23;110(17):6877-82
Authors: Liu B, Staron M, Hong F, Wu BX, Sun S, Morales C, Crosson CE, Tomlinson S, Kim I, Wu D, Li Z
Increasing evidence points to a role for the protein quality control in the endoplasmic reticulum (ER) in maintaining intestinal homeostasis. However, the specific role for general ER chaperones in this process remains unknown. Herein, we report that a major ER heat shock protein grp94 interacts with MesD, a critical chaperone for the Wnt coreceptor low-density lipoprotein receptor-related protein 6 (LRP6). Without grp94, LRP6 fails to export from the ER to the cell surface, resulting in a profound loss of canonical Wnt signaling. The significance of this finding is demonstrated in vivo in that grp94 loss causes a rapid and profound compromise in intestinal homeostasis with gut-intrinsic defect in the proliferation of intestinal crypts, compromise of nuclear β-catenin translocation, loss of crypt-villus structure, and impaired barrier function. Taken together, our work has uncovered the role of grp94 in chaperoning LRP6-MesD in coordinating intestinal homeostasis, placing canonical Wnt-signaling pathway under the direct regulation of the general protein quality control machinery in the ER.
PMID: 23572575 [PubMed - indexed for MEDLINE]
C-type natriuretic peptide protects the retinal pigment epithelium against advanced glycation end product-induced barrier dysfunction.
J Pharmacol Exp Ther. 2013 Jan;344(1):96-102
Authors: Dahrouj M, Alsarraf O, Liu Y, Crosson CE, Ablonczy Z
In diabetic retinopathy, vision loss is usually secondary to macular edema, which is thought to depend on the functional integrity of the blood-retina barrier. The levels of advanced glycation end products in the vitreous correlate with the progression of diabetic retinopathy. Natriuretic peptides (NP) are expressed in the eye and their receptors are present in the retinal pigment epithelium (RPE). Here, we investigated the effect of glycated-albumin (Glyc-alb), an advanced glycation end product model, on RPE-barrier function and the ability of NP to suppress this response. Transepithelial electrical resistance (TEER) measurements were used to assess the barrier function of ARPE-19 and human fetal RPE (hfRPE) monolayers. The monolayers were treated with 0.1-100 μg/ml Glyc-alb in the absence or presence of 1 pM to 100 nM apical atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), or C-type natriuretic peptide (CNP). Glyc-alb induced a significant reduction in TEER within 2 hours. This response was concentration-dependent (EC(50)= 2.3 μg/ml) with a maximal reduction of 40 ± 2% for ARPE-19 and 27 ± 7% for hfRPE at 100 μg/ml 6 hours post-treatment. One hour pretreatment with ANP, BNP, or CNP blocked the reduction in TEER induced by Glyc-alb (100 μg/ml). The suppression of the Glyc-alb response by NP was dependent on the generation of cyclic guanosine monophosphate and exhibited a rank order of agonist potency consistent with the activation of natriuretic-peptide-receptor-2 (NPR2) subtype (CNP >> BNP ≥ ANP). Our data demonstrate that Glyc-alb is effective in reducing RPE-barrier function, and this response is suppressed by NP. Moreover, these studies support the idea that NPR2 agonists can be potential candidates for treating retinal edema in diabetic patients.
PMID: 23086231 [PubMed - indexed for MEDLINE]
Preservation of retina ganglion cell function by morphine in a chronic ocular-hypertensive rat model.
Invest Ophthalmol Vis Sci. 2012;53(7):4289-98
Authors: Husain S, Abdul Y, Crosson CE
PURPOSE: The current study examined if opioid-receptor-activation by morphine can improve retinal function and retinal ganglion cell (RGC) integrity in a chronic glaucoma rat model.
METHODS: IOP was raised in Brown Norway rats by injecting hypertonic saline into the limbal venous system. Rats were treated daily with 1 mg/kg morphine for 28 days at 24-hour intervals; animals were examined for changes in IOP by a TonoLab tonometer. Pattern-ERG (PERG) was obtained in response to contrast-reversal of patterned visual stimuli. RGCs were visualized by fluorogold retrograde-labeling. Changes in the expression pattern of TNF-α and caspases were measured by Western blotting.
RESULTS: A significant IOP elevation was seen as early as 7 days, and maintained for up to 8 weeks, after surgery. PERG amplitudes were significantly reduced in ocular-hypertensive eyes (15.84±0.74 μvolts) when compared with normal eyes (19±0.86 μvolts). PERG deficits in hypertensive eyes were reversed by morphine treatment (18.23±0.78 μvolts; P<0.05). In untreated rats, a 24% reduction in labeled RGCs was measured in the hypertensive eye compared with the normal eye. This reduction in RGC labeling was significantly ameliorated in the presence of morphine. In retinal samples, TNF-α, caspase-8, and caspase-3 expressions were significantly upregulated in ocular hypertensive eyes, but completely inhibited in the morphine-treated animals.
CONCLUSIONS: These data provide evidence that activation of opioid receptors can provide significant improvement in PERG and RGC integrity against glaucomatous injury. Mechanistic data provide clues that activation of one or more opioid receptors can reduce glaucomatous-injury via suppression of TNF-α and caspase activation.
PMID: 22661469 [PubMed - indexed for MEDLINE]
Influence of race and age on aqueous humor levels of transforming growth factor-beta 2 in glaucomatous and nonglaucomatous eyes.
J Ocul Pharmacol Ther. 2011 Oct;27(5):477-80
Authors: Trivedi RH, Nutaitis M, Vroman D, Crosson CE
PURPOSE: To evaluate the influence of race and age on aqueous humor levels of transforming growth factor-beta 2 (TGF-β2).
METHODS: Patients >40 years of age and undergoing cataract or glaucoma surgery without associated significant intraocular pathology were selected for this study. In bilateral cases, only the first operated eye was included for evaluation. At the time of surgery, a small amount of aqueous was withdrawn. The concentration of total TGF-β2 was measured by enzyme-linked immunosorbent assay in duplicate by a masked observer.
RESULTS: Fifty-five aqueous humor samples were analyzed from subjects with an average age of 68.05 ± 10.94 years. Overall median TGF-β2 concentration was 247.03 pg/mL. The median concentration of TGF-β2 was higher in eyes with glaucoma than in eyes without glaucoma (269.39 vs. 165.56 pg/mL, respectively; P = 0.001). Subgroup analysis found no significant difference between African American and Caucasian American subjects in the nonglaucomatous or glaucomatous subgroups. Age showed positive correlation with TGF-β2 in nonglaucomatous eyes (r(2) = 0.44, P = 0.019). No correlation between age and TGF-β2 was noted in the glaucoma group (r(2) = 0.02, P = 0.343).
CONCLUSION: The aqueous humor concentration of TGF-β2 was significantly higher in eyes with glaucoma than in eyes without glaucoma. No significant difference between the aqueous humor levels of TGF-β2 from African American and Caucasian American subjects could be measured. However, a significant and positive correlation between age and aqueous humor concentration of TGF-β2 in the eyes of nonglaucomatous subjects was measured. These results are consistent with the idea that elevated levels of TGF-β2 within the anterior segment contribute to the development of glaucoma. In addition, the increased risk for developing glaucoma as one ages may in part be related to the rise of this cytokine.
PMID: 21034224 [PubMed - indexed for MEDLINE]
Bradykinin activation of extracellular signal-regulated kinases in human trabecular meshwork cells.
Exp Eye Res. 2011 Jun;92(6):495-501
Authors: Webb JG, Yang X, Crosson CE
Bradykinin stimulation of B(2) kinin receptors has been shown to promote matrix metallo-proteinase (MMP) secretion from trabecular meshwork cells and to increase conventional outflow facility. Because acute secretion of MMPs can be dependent on the activity of extracellular signal-regulated MAP kinases (ERK1/2), experiments were performed to determine bradykinin effects on ERK1/2 in cultured human trabecular meshwork cells and the relationship of these effects to MMP-9 release. Treatment of cells with bradykinin produced a rapid 4-to 6-fold increase in ERK1/2 phosphorylation. Stimulation of ERK1/2 activity peaked within 2 min and then declined to control levels by 60 min. The response maximum occurred with 100nM bradykinin and the estimated EC₅₀ was 0.7nM. Treatment of cells with the B₂ kinin receptor agonist, Tyr⁸- bradykinin, also stimulated ERK1/2 phosphorylation while the B₁ agonist, Lys- [Des-Arg⁹]- bradykinin had no significant effect. In addition, activation of ERK1/2 by bradykinin or Tyr⁸- bradykinin was blocked by the selective B₂ receptor antagonist, Hoe-140. Inhibition of MAP kinase kinase (MEK) with U0126 also blocked bradykinin-induced ERK1/2 phosphorylation. Suppression of protein kinase C activity with the nonselective inhibitor, GF109203X, or by down-regulation with phorbol ester, diminished, but did not eliminate, bradykinin activation of ERK1/2. A similar decrease of ERK1/2 stimulation was observed when Src kinase was inhibited by 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2). Finally, blockade of bradykinin-induced ERK1/2 activation substantially reduced the peptide's action to stimulate MMP-9 release into the extracellular environment. The data demonstrate that bradykinin promotes ERK1/2 activation in human trabecular meshwork cells. The effect is mediated by B₂ kinin receptors, involves two different signaling pathways, and results in increased secretion of MMP-9.
PMID: 21426904 [PubMed - indexed for MEDLINE]
Opioid receptor activation: suppression of ischemia/reperfusion-induced production of TNF-α in the retina.
Invest Ophthalmol Vis Sci. 2011 Apr;52(5):2577-83
Authors: Husain S, Liou GI, Crosson CE
PURPOSE: The detrimental role of TNF-α in ischemia-induced tissue damage is known. The authors study examined whether opioid receptor activation alters TNF-α levels in the postischemic retina.
METHODS: Retinal ischemia was induced by raising the intraocular pressure above systolic blood pressure (155-160 mm Hg) for 45 minutes. Rats were pretreated with the opioid receptor agonist morphine (1 mg/kg; intraperitoneally) before injury. Selected animals were pretreated with the opioid antagonist naloxone (3 mg/kg; intraperitoneally). Human optic nerve head (ONH) astrocytes and rat microglial cells were treated with morphine (0.1-1 μM) for 24 hours and then treated with 10 μg/mL or 30 ng/mL lipopolysaccharide (LPS), respectively. TNF-α was measured by ELISA. Opioid receptor subtypes in astrocytes and microglia were determined by Western blot analysis.
RESULTS: There was a time-dependent increase in TNF-α production; the maximum production occurred at 4 hours after ischemia and localized to the inner retinal regions. Ischemia-induced TNF-α production was significantly inhibited by morphine. In astrocytes and microglia, LPS triggered a robust increase in the release of TNF-α, which was significantly inhibited (P < 0.05) by morphine. Naloxone reversed the morphine-induced suppression of TNF-α production in vivo and in vitro. Both ONH astrocytes and microglial cells expressed δ-, κ-, and μ-opioid receptor subtypes.
CONCLUSIONS: These data provide evidence that the production of TNF-α after ischemia/reperfusion injury is an early event and that opioid receptor activation reduces the production of TNF-α. Immunohistochemistry data and in vitro studies provide evidence that ONH astrocytes and microglial cells are the primary sources for the TNF-α production under ischemic/inflammatory conditions. Activation of one or more opioid receptors can reduce ischemic/reperfusion injury by the suppression of TNF-α production.
PMID: 21282567 [PubMed - indexed for MEDLINE]
Human retinal pigment epithelium cells as functional models for the RPE in vivo.
Invest Ophthalmol Vis Sci. 2011;52(12):8614-20
Authors: Ablonczy Z, Dahrouj M, Tang PH, Liu Y, Sambamurti K, Marmorstein AD, Crosson CE
PURPOSE: The two most commonly used in vitro models of the retinal pigment epithelium (RPE) are fetal human RPE (fhRPE) and ARPE-19 cells; however, studies of their barrier properties have produced contradictory results. To compare their utility as RPE models, their morphologic and functional characteristics were analyzed.
METHODS: Monolayers of both cell types were grown on permeable membrane filters. Barrier function and cellular morphology were assessed by transepithelial resistance (TER) measurements and immunohistochemistry. Protein expression was evaluated by immunoblotting and ELISA assays, and retinoid metabolism characterized by HPLC.
RESULTS: Both cultures developed tight junctions. However, only the fhRPE cells were pigmented, uniform in size and shape, expressed high levels of RPE markers, metabolized all-trans retinal, and developed high TER (>400 Ωcm(2)). The net secretion of pigment-epithelium-derived factor (PEDF) was directed apically in both cultures, but fhRPE cells exhibited secretion rates a thousand-fold greater than in ARPE-19 cells. The net secretion of vascular endothelial growth factor (VEGF) was significantly higher in fhRPE cultures and the direction of this secretion was basolateral; while net secretion was apical in ARPE-19 cells. In fresh media, VEGF-E reduced TER in both cultures; however, in conditioned media fhRPE cells did not respond to VEGF-E administration, but retreatment of the conditioned media with anti-PEDF antibodies allowed fhRPE cells to fully respond to VEGF-E.
CONCLUSIONS: Properties of fhRPE cells align with a functionally normal RPE in vivo, while ARPE-19 cells resemble a pathologic or aged RPE. These results suggest a utility for both cell types in understanding distinct, particular aspects of RPE function.
PMID: 21960553 [PubMed - indexed for MEDLINE]
Inhibition of histone deacetylase protects the retina from ischemic injury.
Invest Ophthalmol Vis Sci. 2010 Jul;51(7):3639-45
Authors: Crosson CE, Mani SK, Husain S, Alsarraf O, Menick DR
PURPOSE. The pathogenesis of retinal ischemia results from a series of events involving changes in gene expression and inflammatory cytokines. Protein acetylation is an essential mechanism in regulating transcriptional and inflammatory events. The purpose of this study was to investigate the neuroprotective action of the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) in a retinal ischemic model. METHODS. To investigate whether HDAC inhibition can reduce ischemic injury, rats were treated with TSA (2.5 mg/kg intraperitoneally) twice daily on days 0, 1, 2, and 3. Seven days after ischemic injury, morphometric and electroretinographic (ERG) analyses were used to assess retinal structure and function. Western blot and immunohistochemical analyses were used to evaluate TSA-induced changes in histone-H3 acetylation and MMP secretion. RESULTS. In vehicle-treated animals, ERG a- and b-waves from ischemic eyes were significantly reduced compared with contralateral responses. In addition, histologic examination of these eyes revealed significant degeneration of inner retinal layers. In rats treated with TSA, amplitudes of ERG a- and b-waves from ischemic eyes were significantly increased, and normal inner retina morphology was preserved. Ischemia also increased the levels of retinal TNF-alpha, which was blocked by TSA treatment. In astrocyte cultures, the addition of TNF-alpha (10 ng/mL) stimulated the secretion of MMP-1 and MMP-3, which were blocked by TSA (100 nM). CONCLUSIONS. These studies provide the first evidence that suppressing HDAC activity can protect the retina from ischemic injury. This neuroprotective response is associated with the suppression of retinal TNF-alpha expression and signaling. The use of HDAC inhibitors may provide a novel treatment for ischemic retinal injury.
PMID: 20164449 [PubMed - indexed for MEDLINE]