Deletion of Fgfr2 in Ductal Basal Epithelium With Tamoxifen Induces Obstructive Meibomian Gland Dysfunction.

Purpose: Fibroblast growth factor receptor 2 (Fgfr2) is crucial for the homeostasis of meibomian gland (MG). However, the role of Fgfr2 in MG ductal epithelial progenitors remains to be delineated. Herein, we created a new transgenic mouse model with conditional deletion of Fgfr2 from MG ductal progenitors and investigated the cell-specific role in the pathogenesis of obstructive meibomian gland dysfunction.

Meibomian gland stem/progenitor cells: The hunt for gland renewal.

Meibomian glands (MGs) secrete lipid (meibum) onto the ocular surface to form the outermost layer of the tear film. Proper meibum secretion is essential for stabilizing the tear film, reducing aqueous tear evaporation, and maintaining the homeostasis of the ocular surface. Atrophy of MG as occurs with aging, leads to reduction of meibum secretion, loss of ocular surface homeostasis and evaporative dry eye disease (EDED).

Spontaneous acinar and ductal regrowth after meibomian gland atrophy induced by deletion of FGFR2 in a mouse model.

Purpose: We have demonstrated that deletion of fibroblast growth factor receptor 2 gene (Fgfr2) leads to Meibomian gland (MG) atrophy in an inducible conditional knockout mouse model, referred as Fgfr2. Herein, we investigated whether MG spontaneously recovers after atrophy in this model.

Methods: Two months old Fgfr2 mice were injected peritoneally once or twice of doxycycline (Dox) at 80 μg/gm of body weight to induce MG atrophy of various severities via Fgfr2 deletion.

Histopathology and selective biomarker expression in human meibomian glands.

Background/aims: Meibomian gland dysfunction (MGD) is the most common form of evaporative dry eye disease, but its pathogenesis is poorly understood. This study examined the histopathological features of meibomian gland (MG) tissue from cadaver donors to identify potential pathogenic processes that underlie MGD in humans.

Methods: Histological analyses was performed on the MGs in the tarsal plates dissected from four cadaver donors, two young and two old adults, including a 36-year-old female (36F) and three males aged 30, 63 and 64 years (30M, 63M and 64M).

Fibroblast Growth Factor Receptor 2 (FGFR2) Is Required for Meibomian Gland Homeostasis in the Adult Mouse.

Purpose: Little is known about the signaling mechanisms controlling meibomian gland (MG) homeostasis and the pathogenic processes leading to MG atrophy and dysfunction in dry eye disease (DED). We investigated the role of fibroblast growth factor receptor 2 (FGFR2) in the MG homeostasis of adult mice.

Methods: A triple transgenic mouse strain (Krt14-rtTA; tetO-Cre; Fgfr2flox/flox), referred to as Fgfr2CKO mice, was generated in which the Fgfr2 gene is ablated by Cre recombinase in keratin 14 (Krt14)-expressing epithelial cells on doxycycline (Dox) induction.

Regulation of c-Maf and αA-Crystallin in Ocular Lens by Fibroblast Growth Factor Signaling.

Fibroblast growth factor (FGF) signaling regulates a multitude of cellular processes, including cell proliferation, survival, migration, and differentiation. In the vertebrate lens, FGF signaling regulates fiber cell differentiation characterized by high expression of crystallin proteins. However, a direct link between FGF signaling and crystallin gene transcriptional machinery remains to be established.

Unfolded-protein response-associated stabilization of p27(Cdkn1b) interferes with lens fiber cell denucleation, leading to cataract.

Failure of lens fiber cell denucleation (LFCD) is associated with congenital cataracts, but the pathobiology awaits elucidation. Recent work has suggested that mechanisms that direct the unidirectional process of LFCD are analogous to the cyclic processes associated with mitosis. We found that lens-specific mutations that elicit an unfolded-protein response (UPR) in vivo accumulate p27(Cdkn1b), show cyclin-dependent kinase (Cdk)-1 inhibition, retain their LFC nuclei, and are cataractous.

Fibroblast growth factor receptor 2 (FGFR2) is required for corneal epithelial cell proliferation and differentiation during embryonic development.

Fibroblast growth factors (FGFs) play important roles in many aspects of embryonic development. During eye development, the lens and corneal epithelium are derived from the same surface ectodermal tissue. FGF receptor (FGFR)-signaling is essential for lens cell differentiation and survival, but its role in corneal development has not been fully investigated.

Histone deacetylase inhibitors trichostatin A and vorinostat inhibit TGFβ2-induced lens epithelial-to-mesenchymal cell transition.

Purpose: Posterior capsule opacification (PCO) after cataract surgery is due in part to proliferation of the adhering lens epithelial cells and transdifferentiation into mesenchymal cells. The histone deacetylase (HDAC) inhibitors, trichostatin A (TSA) and vorinostat (suberoylanilidehydroxamic acid [SAHA]) are known to modulate cell proliferation and epithelial-mesenchymal transition (EMT). Studies have shown that TGFβ2 can induce EMT similar to that seen during PCO.

Frs2α enhances fibroblast growth factor-mediated survival and differentiation in lens development.

Most growth factor receptor tyrosine kinases (RTKs) signal through similar intracellular pathways, but they often have divergent biological effects. Therefore, elucidating the mechanism of channeling the intracellular effect of RTK stimulation to facilitate specific biological responses represents a fundamental biological challenge. Lens epithelial cells express numerous RTKs with the ability to initiate the phosphorylation (activation) of Erk1/2 and PI3-K/Akt signaling.

Activation of unfolded protein response in transgenic mouse lenses.

Purpose: Overloading of unfolded or misfolded proteins in the endoplasmic reticulum (ER) can cause ER stress and activate the unfolded protein response (UPR) in the cell. The authors tested whether transgene overexpression in the mouse lens would activate the UPR.

Methods: Transgenic mice expressing proteins that either enter the ER secretory pathway or are synthesized in cytosol were selected.

Sef is a negative regulator of fiber cell differentiation in the ocular lens.

Growth factor signaling, mediated via receptor tyrosine kinases (RTKs), needs to be tightly regulated in many developmental systems to ensure a physiologically appropriate biological outcome. At one level this regulation may involve spatially and temporally ordered patterns of expression of specific RTK signaling antagonists, such as Sef (similar expression to fgfs). Growth factors, notably FGFs, play important roles in development of the vertebrate ocular lens.

Induction of corneal myofibroblasts by lens-derived transforming growth factor beta1 (TGFbeta1): a transgenic mouse model.

Purpose: Transforming growth factor beta (TGFbeta) is an important cytokine in corneal development and wound healing. Transgenic mice that express an active form of human TGFbeta1 driven by a lens-specific promoter were used in the current study to determine the biological effects of lens-derived TGFbeta1 on postnatal corneal development and homeostasis.

Methods: The postnatal corneal changes in the TGFbeta1 transgenic mice were examined by fluorescein labeling and histology.

Indoleamine 2,3-dioxygenase overexpression causes kynurenine-modification of proteins, fiber cell apoptosis and cataract formation in the mouse lens.

Indoleamine 2,3-dioxygenase (IDO) is the first enzyme in the kynurenine pathway. The kynurenines formed in this pathway chemically modify proteins and cause apoptosis in cells. Evidence suggests that kynurenines and their protein modifications are involved in cataract formation, but this has yet to be directly demonstrated.

Rho GDP dissociation inhibitor-mediated disruption of Rho GTPase activity impairs lens fiber cell migration, elongation and survival.

To explore the role of the Rho GTPases in lens morphogenesis, we overexpressed bovine Rho GDP dissociation inhibitor (Rho GDI alpha), which serves as a negative regulator of Rho, Rac and Cdc42 GTPase activity, in a lens-specific manner in transgenic mice. This was achieved using a chimeric promoter of delta-crystallin enhancer and alpha A-crystallin, which is active at embryonic day 12. Several individual transgenic (Tg) lines were obtained, and exhibited ocular specific phenotype comprised of microphthalmic eyes with lens opacity.

Elevated insulin signaling disrupts the growth and differentiation pattern of the mouse lens.

Purpose: Insulin and insulin-like growth factors (IGFs) are putative regulators of cell proliferation and differentiation during lens development. Transgenic mice that overexpress IGF-1 in the lens have been previously described. To further understand the ocular functions of this growth factor family, the in vivo effects of insulin expression on lens development were investigated using transgenic mice.

Vitamin C mediates chemical aging of lens crystallins by the Maillard reaction in a humanized mouse model.

Senile cataracts are associated with progressive oxidation, fragmentation, cross-linking, insolubilization, and yellow pigmentation of lens crystallins. We hypothesized that the Maillard reaction, which leads browning and aroma development during the baking of foods, would occur between the lens proteins and the highly reactive oxidation products of vitamin C. To test this hypothesis, we engineered a mouse that selectively overexpresses the human vitamin C transporter SVCT2 in the lens.

Ras signaling is essential for lens cell proliferation and lens growth during development.

The vertebrate ocular lens is a simple and continuously growing tissue. Growth factor-mediated receptor tyrosine kinases (RTKs) are believed to be required for lens cell proliferation, differentiation and survival. The signaling pathways downstream of the RTKs remain to be elucidated.

Targeted gene expression in the chicken eye by in ovo electroporation.

Purpose: The chicken embryo lens is a classical model system for developmental and cell biology studies. To understand the molecular mechanisms that underlie the morphological changes that occur during lens development, it is important to develop an effective gene transfer method that permits the analysis of gene functions in vivo. In ovo electroporation has been successfully used for introducing DNA into neural and mesenchymal tissues of chicken embryos.

Activated Ras induces lens epithelial cell hyperplasia but not premature differentiation.

Growth factor signaling is implicated in the regulation of lens cell proliferation and differentiation during development. Activation of growth factor receptor tyrosine kinases is known to activate Ras proteins, small GTP-binding proteins that function as part of the signal transduction machinery. In the present study, we examined which classical Ras genes are expressed in lens cells during normal development and whether expression of an activated version of Ras is sufficient to induce either lens cell proliferation or fiber cell differentiation in transgenic mice.

Chick delta1-crystallin enhancer influences mouse alphaA-crystallin promoter activity in transgenic mice.

Purpose: Both the -366/+43 and the -282/+43 mouse alphaA-crystallin (or alphaA) promoters have been effective at driving transgene expression in lens fiber cells, but not in lens epithelium. Because the chick delta1-crystallin gene is expressed in lens epithelial cells, an enhancer was borrowed from this gene and linked to the alphaA promoter. This heterogenic enhancer/promoter construct was tested in transgenic mice to see whether it was active in both lens epithelium and fiber cells while retaining lens specificity.

Ectopic Pax6 expression disturbs lens fiber cell differentiation.

Purpose: Pax6 is a transcription factor necessary for the specification and subsequent formation of the ocular lens. It is expressed in all lens cells at early stages of development. After lens formation, Pax6 expression is maintained in the lens epithelium, whereas its level abruptly decreases in differentiated fiber cells.

Expression patterns of cytochrome P4501B1 (Cyp1b1) in FVB/N mouse eyes.

Homozygous and compound heterozygous mutations in cytochrome P4501B1 (CYP1B1) cause primary congenital glaucoma (PCG) in humans. It is hypothesized that developmental anomalies of the trabecular meshwork prevent appropriate drainage of the aqueous humor and cause PCG in human patients. In this report, we studied the expression patterns of Cyp1b1 in the eye of albino FVB/N mouse at different developmental stages.

Systematic analysis of E-, N- and P-cadherin expression in mouse eye development.

Cadherins are a family of Ca(2+)-dependent cell adhesion molecules. Through their homophilic binding interactions, cadherins play important roles in tissue formation and maintenance during development. Here the authors compare the expression patterns of the three classical cadherins, E-, N- and P-cadherin, during mouse eye development from embryonic day 9.