Transforming growth factor-beta2 inhibition of corneal endothelial proliferation mediated by prostaglandin

CHIR99021 balance TGFβ1 induced human corneal endothelial-to-mesenchymal transition to favor corneal endothelial cell proliferation

Corneal endothelial cells (CECs) play a major role in the maintenance of stromal hydration via the barrier and pump function for clear vision. Adult CEC cannot regenerate after injury. CECs cultured in vitro can undergo mitosis but may undergo corneal endothelial-to-mesenchymal transition (EnMT) and lose their endothelial characteristics. In this study, we examined the effects of CHIR99201 on transforming growth factor beta-1(TGFβ1)-induced EnMT in human CEC (hCECs) lines. CHIR99021 kept hCECs in the hexagonal shape and could downregulate the EnMT markers alpha-smooth muscle actin (α-SMA) and fibronectin (FN1), meanwhile maintained the hCECs function markers Na⁺/K⁺-ATPase and zonula occludens-1 (ZO-1) at levels comparable to those in the normal control. Interestingly, we found that the combination of CHIR99021 and TGFβ1 at appropriate concentrations would significantly promote the proliferation and migration of hCECs. These effects may be related to the inhibition of RhoA or Rac1, as well as the activation of Wnt and Erk pathway, with a calcium homeostasis. Our findings indicate that CHIR99021 inhibit EnMT and that the combination of CHIR99021 and TGFβ1 may provide new ideas for corneal endothelial regeneration and wound healing.

Identification of prostamides, fatty acyl ethanolamines, and their biosynthetic precursors in rabbit cornea

Arachidonoyl ethanolamine (anandamide) and pros-taglandin ethanolamines (prostamides) are biologically active derivatives of arachidonic acid. Although available through different precursor phospholipids, there is considerable overlap between the biosynthetic pathways of arachidonic acid-derived eicosanoids and anandamide-derived prostamides. Prostamides exhibit physiological actions and are involved in ocular hypotension, smooth muscle contraction, and inflammatory pain. Although topical application of bimatoprost, a structural analog of prostaglandin F2α ethanolamide (PGF2α-EA), is currently a first-line treatment for ocular hypertension, the endogenous production of prostamides and their biochemical precursors in corneal tissue has not yet been reported. In this study, we report the presence of anandamide, palmitoyl-, stearoyl-, α-linolenoyl docosahexaenoyl-, linoleoyl-, and oleoyl-ethanolamines in rabbit cornea, and following treatment with anandamide, the formation of PGF2α-EA, PGE2-EA, PGD2-EA by corneal extracts (all analyzed by LC/ESI-MS/MS). A number of N-acyl phosphatidylethanolamines, precursors of anandamide and other fatty acyl ethanolamines, were also identified in corneal lipid extracts using ESI-MS/MS. These findings suggest that the prostamide and fatty acid ethanolamine pathways are operational in the cornea and may provide valuable insight into corneal physiology and their potential influence on adjacent tissues and the aqueous humor.

Effect of amniotic fluid on the in vitro culture of human corneal endothelial cells

The present study was designed to evaluate the effects of human amniotic fluid (HAF) on the growth of human corneal endothelial cells (HCECs) and to establish an in vitro method for expanding HCECs. HCECs were cultured in DMEM-F12 supplemented with 20% fetal bovine serum (FBS). Confluent monolayer cultures were trypsinized and passaged using either FBS- or HAF-containing media. Cell proliferation and cell death ELISA assays were performed to determine the effect of HAF on cell growth and viability. The identity of the cells cultured in 20% HAF was determined using immunocytochemistry (ICC) and real-time reverse transcription polymerase chain reaction (RT-PCR) techniques to evaluate the expression of factors that are characteristic of HCECs, including Ki-67, Vimentin, Na+/K+-ATPase and ZO-1. HCEC primary cultures were successfully established using 20% HAF-containing medium, and these cultures demonstrated rapid cell proliferation according to the cell proliferation and death ELISA assay results. The ICC and real time RT-PCR results indicated that there was a higher expression of Na+/K+-ATPase and ZO-1 in the 20% HAF cell cultures compared with the control (20% FBS) (P < 0.05). The 20% HAF-containing medium exhibited a greater stimulatory effect on HCEC growth and could represent a potential enriched supplement for HCEC regeneration studies.

Intraocular pressure, specular microscopy, and prostaglandin E2 concentration in dogs with mature and hypermature cataract

This study aimed to evaluate and correlate intraocular pressure (IOP), endothelial cell density (CD), and hexagonality (HEX), and the aqueous humor prostaglandin E2 (PGE2 ) concentration in dogs with mature (MG, n = 8) and hypermature (HG, n = 8) cataracts. Eight laboratory beagles with no ocular abnormalities were included as a control group (CG). The IOP was measured using a digital applanation tonometer. Noncontact specular microscopy was used to evaluate CD and HEX. Samples of aqueous humor were used to determine prostaglandin E2 concentration using enzyme-linked immunoassay. Data were compared by anova and Bonferroni's multiple comparison test, and possible correlations among the PGE2 aqueous concentration and corneal endothelium cell parameters were assessed by Person's test (P < 0.05). Average values of IOP (P = 0.45) and CD (P = 0.39) were not significantly different between MG, HM, and CG. Average values of HEX were lower, and PGE2 concentration was increased in the MG and HG in comparison with CG (P < 0.05); however, such parameters did not change significantly between MG and HG (P > 0.05). PGE2 values did not correlate with IOP, CD, and HEX in any group (P > 0.05). Although there were a small number of dogs studied, our results demonstrated that cataract progression from mature to hypermature did not have a significant change in PGE2 aqueous concentration, IOP, corneal endothelial cell count, or morphology. In addition, PGE2 concentration was not correlated with parameters of the corneal endothelium or IOP in dogs with mature or hypermature cataracts.

[The irido-corneo-endothelial syndrome. The loss of the control of corneal endothelial cell cycle. A review]

The three major symptoms of the irido-corneo-endothelial syndrome are the alterations of the corneal endothelium and of the iris with a loss of the regulation of the cell cycle, and the progressive obstruction of the irido-corneal angle. This rare pathology attacks mainly young adult women. Most of the symptoms and complications originate from the excessive proliferation of the corneal endothelial cells accompanied by the evolution of their phenotype towards that of the epithelial cells. In normal conditions the corneal endothelial cells do not divide, they are blocked in the G1 stage of the cell cycle, mainly because of the action of the inhibitors of cyclin-dependent kinases. Still these cells retain a good capacity for proliferation, which can be induced by the down-regulation of the expression of the inhibitors of the cyclin-dependent kinases. This proliferative capacity declines with age and is also different according to the localization of the cells: it is more intense with those originating from the central area then in those from the peripheral area of the cornea. The age-related decline of the proliferative capacity is not due to the shortening of the telomers, but to the stress-induced accelerated senescence of the cells.

Proliferative capacity of corneal endothelial cells

The corneal endothelial monolayer helps maintain corneal transparency through its barrier and ionic "pump" functions. This transparency function can become compromised, resulting in a critical loss in endothelial cell density (ECD), corneal edema, bullous keratopathy, and loss of visual acuity. Although penetrating keratoplasty and various forms of endothelial keratoplasty are capable of restoring corneal clarity, they can also have complications requiring re-grafting or other treatments. With the increasing worldwide shortage of donor corneas to be used for keratoplasty, there is a greater need to find new therapies to restore corneal clarity that is lost due to endothelial dysfunction. As a result, researchers have been exploring alternative approaches that could result in the in vivo induction of transient corneal endothelial cell division or the in vitro expansion of healthy endothelial cells for corneal bioengineering as treatments to increase ECD and restore visual acuity. This review presents current information regarding the ability of human corneal endothelial cells (HCEC) to divide as a basis for the development of new therapies. Information will be presented on the positive and negative regulation of the cell cycle as background for the studies to be discussed. Results of studies exploring the proliferative capacity of HCEC will be presented and specific conditions that affect the ability of HCEC to divide will be discussed. Methods that have been tested to induce transient proliferation of HCEC will also be presented. This review will discuss the effect of donor age and endothelial topography on relative proliferative capacity of HCEC, as well as explore the role of nuclear oxidative DNA damage in decreasing the relative proliferative capacity of HCEC. Finally, potential new research directions will be discussed that could take advantage of and/or improve the proliferative capacity of these physiologically important cells in order to develop new treatments to restore corneal clarity.

Regulation of endothelial cell functions by basement membrane- and arachidonic acid-derived products

Angiogenesis, the formation of new blood vessels from preexisting vasculature, is required for normal physiological as well as pathological events. The angiogenic process requires endothelial cells to proliferate, migrate, and undergo tubulogenesis. These multistep processes necessitate secretion of pro-angiogenic growth factors, activation of specific intracellular signaling, and interaction of endothelial cells with basement membrane (BM) extracellular matrix components. The generation and release of angiogenic molecules are highly regulated and are influenced by numerous factors, including BM-derived fragments, proteolytic enzymes, as well as metabolites of arachidonic acid (AA). The interactions between these key modulators of angiogenesis is extremely complex, as AA metabolites can regulate the synthesis of soluble angiogenic factors, BM components, as well as enzymes capable of cleaving BM components, which result in the generation of pro- and/or anti-angiogenic products. Furthermore, some BM-derived fragments can alter the expression of AA-converting enzymes and consequently the synthesis of angiogenic factors. In this review we describe the relationship between BM components and AA metabolites with respect to the regulation of endothelial cell functions in health and disease.

In vitro culture of human fetal corneal endothelial cells

PURPOSE

To explore and optimize a proper culture system for human fetal corneal endothelial cells (hFCECs), including the methods of primary culture, passage and cryopreservation.

METHODS

Fresh fetal corneas were explanted to propagate primary corneal endothelial cells. The cells were cultured in DMEM/F-12 supplemented with 10% fetal bovine serum (FBS) in the absence or presence of the extracts from bovine corneal endothelium cells (bCECs), and the cells were identified with immunocytochemical staining. The passage and cryopreservation of hFCECs were optimized according to previous reports on adult corneal endothelial cells.

RESULTS

Using the explant culture method, hFCECs migrated successfully within 3 days and assumed polygonal-shaped corneal endothelial morphology. The optimizing methods were 0.125% trypsin + 0.02% EDTA for passage and 10% DMSO + 90% FBS for cryopreservation. Recovered hFCECs from cryopreservation remained typical morphology and immunological markers of corneal endothelial cells, including positive staining of NSE, Nestin, Ki67 and ZO-1, and negative staining of CK3/12, which demonstrated that they retained the characterizations of corneal endothelial cells and proliferative capacity. Moreover, the extracts from bCECs can promote the proliferative capacity of hFCECs significantly, while maintaining their typical endothelial morphology.

CONCLUSIONS

The culture conditions of human fetal corneal endothelial cells were firstly optimized, including the primary culture, passage and cryopreservation. Meanwhile, we confirmed that the extracts from bovine corneal endothelium promoted the proliferative capacity while maintaining the morphology of hFCECs in vitro.

Significance of lipid mediators in corneal injury and repair

Corneal injury induces an inflammatory reaction and damages the sensory nerves that exert trophic influences in the corneal epithelium. Alterations in normal healing disrupt the integrity and function of the tissue with undesirable consequences, ranging from dry eye and loss of transparency to ulceration and perforation. Lipids play important roles in this complex process. Whereas lipid mediators such as platelet activating factor (PAF) and cyclooxygenease-2 metabolites contribute to tissue damage and neovascularization, other mediators, such as the lipoxygenase (LOX) derivatives from arachidonic acid, 12- and 15-hydroxy/hydroperoxyeicosatetraenoic acids, and lipoxin A4, act as second messengers for epidermal growth factor to promote proliferation and repair. Stimulation of the cornea with pigment epithelial derived factor in the presence of docosahexaenoic acid gives rise to the synthesis of neuroprotectin D1, a derivative of LOX activity, and increases regeneration of corneal nerves. More knowledge about the role that lipids play in corneal wound healing can provide insight into the development of new therapeutic approaches for treating corneal injuries. PAF antagonists, lipoxins, and neuroprotectins can be effective therapeutic tools for maintaining the integrity of the cornea.

Cytotoxicity of silicone oil on cultivated human corneal endothelium

BACKGROUND AND OBJECTIVE

To investigate the cytotoxic effects of silicone oil on the cultivated human corneal endothelial cells (CEs).

METHODS

We cultured human CE and passed them in insert wells that allowed the apical side of CE monolayer in contact with the silicone oil. The tested silicone oils were of two different viscosities, 1,000 and 5,000 centistoke (CS). MTS proliferation bioassay and calcein-acetoxymethyl ester (CAM)-ethidium homodimer staining were performed to evaluate cell viability after CEs were co-cultured with silicone oils for 48 h. Apoptosis of CEs was evaluated by TdT-mediated dUTP nick-end labelling (TUNEL) stain.

RESULTS

The MTS bioassay showed that contact of silicone oil inhibited CE proliferation. The higher viscosity (5,000 CS) silicone oil suppressed cell cycling significantly more than the lower viscosity (1,000 CS) silicone oil. CAM-ethidium homodimer staining revealed CE death, 9.1+/-0.1% (1,000 CS silicone oil) and 41.6+/-0.4% (5,000 CS), but apoptosis played only minor role in silicone oil toxicity, 1.7+/-0.1% (1,000 CS silicone oil) and 9.4+/-0.1% (5,000 CS).

CONCLUSIONS

Silicone oil is cytotoxic to cultivated human CEs. Avoiding the forward migration of silicone oil to the anterior chamber and corneal CE contact is critical in preventing silicone oil-associated keratopathy. Silicone oil should be removed as early as possible once the goal of tamponade has been achieved.

Prostaglandin E2-EP4 receptor promotes endothelial cell migration via ERK activation and angiogenesis in vivo

Prostaglandin E2 (PGE(2)), a major product of cyclooxygenase, exerts its functions by binding to four G protein-coupled receptors (EP1-4) and has been implicated in modulating angiogenesis. The present study examined the role of the EP4 receptor in regulating endothelial cell proliferation, migration, and tubulogenesis. Primary pulmonary microvascular endothelial cells were isolated from EP4(flox/flox) mice and were rendered null for the EP4 receptor with adenoCre virus. Whereas treatment with PGE(2) or the EP4 selective agonists PGE(1)-OH and ONO-AE1-329 induced migration, tubulogenesis, ERK activation and cAMP production in control adenovirus-transduced endothelial EP4(flox/flox) cells, no effects were seen in adenoCre-transduced EP4(flox/flox) cells. The EP4 agonist-induced endothelial cell migration was inhibited by ERK, but not PKA inhibitors, defining a functional link between PGE(2)-induced endothelial cell migration and EP4-mediated ERK signaling. Finally, PGE(2), as well as PGE(1)-OH and ONO-AE1-329, also promoted angiogenesis in an in vivo sponge assay providing evidence that the EP4 receptor mediates de novo vascularization in vivo.

TGF-beta2 inhibits AKT activation and FGF-2-induced corneal endothelial cell proliferation

The corneal endothelial cells form a boundary layer between anterior chamber and cornea. This single cell layer is important to maintain cornea transparency by eliciting net fluid transport into the anterior chamber. Injuries of the corneal endothelial layer in humans lead to corneal swelling and translucence. This hindrance is thought to be due to limited proliferative capacity of the endothelial layer. Fibroblast growth factor 2 (FGF-2) and transforming growth factor-beta 2 (TGF-beta2) are both found in aqueous humor, and these two cytokines promote and inhibit cell growth, respectively. The intracellular signaling mechanisms by which TGF-beta2 suppresses the mitogenic response to FGF-2, however, remain unclear. We have addressed this question by investigating potential crosstalk between FGF-2-induced and TGF-beta2-regulated intracellular signaling events in cultured bovine corneal endothelial (BCE) cells. We found that TGF-beta2 and FGF-2 oppositely affect BCE cell proliferation and TGF-beta2 can override the stimulating effects of FGF-2 by increasing COX-2 expression in these cells. Consistent with these findings, overexpression of COX-2 significantly reduced FGF-2-induced cell proliferation whereas a COX-2 specific inhibitor NS398 reversed the effect of TGF-beta2 on FGF-2-induced cell proliferation. The COX-2 product prostaglandin E2 (PGE-2) blocks FGF-2-induced cell proliferation. Whereas FGF-2 stimulates cell proliferation by activating the AKT pathway, TGF-beta2 and PGE-2 both inhibit this pathway. In accordance with the effect of PGE-2, cAMP also inhibits FGF-2-induced AKT activation. These findings suggest that the mitogenic response to FGF-2 in vivo in the corneal endothelial layer may be inhibited by TGF-beta2-induced suppression of the PI3-kinase/AKT signaling pathway.