Ultrastructural observations on the development of the human conjunctival epithelium

Pathophysiology of aniridia-associated keratopathy: Developmental aspects and unanswered questions

Aniridia, a rare congenital disease, is often characterized by a progressive, pronounced limbal insufficiency and ocular surface pathology termed aniridia-associated keratopathy (AAK). Due to the characteristics of AAK and its bilateral nature, clinical management is challenging and complicated by the multiple coexisting ocular and systemic morbidities in aniridia. Although it is primarily assumed that AAK originates from a congenital limbal stem cell deficiency, in recent years AAK and its pathogenesis has been questioned in the light of new evidence and a refined understanding of ocular development and the biology of limbal stem cells (LSCs) and their niche. Here, by consolidating and comparing the latest clinical and preclinical evidence, we discuss key unanswered questions regarding ocular developmental aspects crucial to AAK. We also highlight hypotheses on the potential role of LSCs and the ocular surface microenvironment in AAK. The insights thus gained lead to a greater appreciation for the role of developmental and cellular processes in the emergence of AAK. They also highlight areas for future research to enable a deeper understanding of aniridia, and thereby the potential to develop new treatments for this rare but blinding ocular surface disease.

[Importance of investigation of fetal eyes : Supplement to fetal autopsy]

The investigation of fetal eyes is a subspecialty, which is performed by only a few ophthalmic pathologists and pathologists in specialized centers. If a certain fetal syndrome is suspected, the fetal eyes should be removed and submitted for ophthalmic pathological investigation in a specialized center. This can provide additional diagnostic information allowing a final classification of a syndrome and the comprehensive genetic counselling of parents with respect to future pregnancies. This article provides an overview of the histopathological findings in fetal eyes, which are of particular relevance for the pediatric pathological autopsy. In addition, the basic points of ocular development, the preparation of fetal eyes and frequent artifacts are presented.

Follow up of patients with ocular scarring secondary to LOC syndrome treated by amniotic membrane transplantation

AIMS

To document and discuss the long term outcome of a new ophthalmic treatment for laryngo-onycho-cutaneous (LOC) syndrome.

METHODS

Two children were treated by excision of ocular granulation tissue and ocular surface rehabilitation with frozen amniotic membrane (AM). The clinical course of both patients was followed and documented at 2 years and 4 years following the surgery.

RESULTS

Patient 1 demonstrated limited recurrence of granulation tissue at 10 months. After 36 months, re-growth of granulation and scar tissue required a further three subsequent operations to the right eye in an attempt to keep the optical axis clear. 4 years postoperatively, neither eye has a clear visual axis. In contrast similar surgery for the right eye of patient 2 has been highly successful, with only very limited non-progressive recurrence after 2 years of follow up. The operation to the left eye has been similarly effective although the follow up is only 6 months.

CONCLUSIONS

Ocular surface rehabilitation with AM is the first partially effective treatment for the eye complications of LOC syndrome. The surprising benefit from AM may stem from the primary pathology of the condition. LOC syndrome is caused by a genetic defect resulting in an unusual N-terminal deletion of the alpha3a chain of the basement membrane protein laminin 5. One mechanism through which AM transplantation may act to reduce ocular scarring in this disease is to supplement the abnormal secreted laminin 5 with healthy transplanted laminin. Despite its initial efficacy one episode of AM treatment does not guarantee long term control of the scarring process and variations in AM graft efficacy may be related to other complicating factors such as limbal stem cell deficiency or severity of the initial scarring process.

Cholinergic agonists transactivate EGFR and stimulate MAPK to induce goblet cell secretion

Conjunctival goblet cells are the primary source of mucins in the mucous layer, the innermost layer of the tear film. Conjunctival goblet cell mucin secretion is under neural control because exogenous addition of parasympathetic agonists stimulates goblet cell secretion. To elucidate the intracellular signal pathways used by cholinergic agonists to stimulate goblet cell mucin secretion, we determined whether p42/p44 mitogen-activated protein kinase (MAPK) is activated during cholinergic agonist-stimulated mucin secretion. Rat conjunctiva was removed, preincubated with or without antagonists, and stimulated with the cholinergic agonist carbachol (10(-4) M). Carbachol statistically significantly stimulated the phosphorylation of MAPK in a time- and concentration-dependent manner. U-0126, an inhibitor of MAPK activation, completely inhibited both the activation of MAPK and goblet cell secretion stimulated by carbachol. The M(1) muscarinic antagonist pirenzepine, the M(2) muscarinic antagonist gallamine, and the M(1)/M(3) muscarinic receptor antagonist N-(3-chloropropyl)-4-piperidinyl diphenylacetate (4-DAMP) also inhibited carbachol-stimulated MAPK activation. Increasing the intracellular Ca(2+) concentration with a Ca(2+) ionophore increased MAPK activation, and chelation of extracellular Ca(2+) inhibited carbachol-stimulated activation. Carbachol also increased tyrosine phosphorylation of Pyk2, p60Src, and the epidermal growth factor receptor (EGFR). The Src inhibitor PP1 and the EGFR inhibitor AG-1478 completely inhibited carbachol-stimulated MAPK activation. AG-1478 also inhibited goblet cell secretion. We conclude that carbachol transactivates the EGFR to activate MAPK, leading to conjunctival goblet cell secretion. In addition, carbachol also activates Pyk2 and p60Src that could play a role in the transactivation of the EGFR.

Morphological differentiation of the conjunctival goblet cells in the chick (Gallus domesticus)

BACKGROUND

These is no consensus in the literature regarding the differentiation of conjunctival goblet cells in vertebrates.

METHOD

The conjunctival epithelium of the chick was studied before and after hatching in order to demonstrate the morphological evolution of the goblet cells. The entire conjunctiva was processed for light microscopy either on semithin sections stained with toluidine blue-pironine or on traditional sections stained with Alcian blue pH 2.5-PAS.

RESULTS

It was possible to demonstrate that goblet cells underwent remarkable changes in their secretory activity. At 12 h after hatching, isolated Alcian blue-positive cells were present in the fornix. At 24 h after hatching, cells positive for both Alcian blue and PAS were scattered among epithelial cells. Two days after hatching, cells which reacted positively only to PAS were also present.

CONCLUSION

It is suggested that the differentiation of conjunctival goblet cells occurs first in the fornix, probably due to the particular vascular environment of this region, and then spreads all over the conjunctiva.

Characterization of epithelial primary cultures from human conjunctiva

Primary cultures of human epithelial cells from normal conjunctiva were developed and characterized to determine whether they retained epithelial characteristics. Conjunctival explants were obtained from the upper fornix of healthy donors and cultured in supplemented DMEM/F-12 medium for 5 days. The epithelial outgrowth was maintained for an additional 10 days. Primary cultures were then processed for light microscopy, transmission and scanning electron microscopy (TEM, SEM), and immunocytochemistry. They exhibited typical features of conjunctival epithelium on light microscopy (polygonal morphology, intimate cohesion, production of mucins), TEM (abundant desmosomes, keratin bundles, granules, microvilli), SEM (polygonal shape, microvilli, intimate cohesion), and immunocytochemistry (positivity for the receptor of epidermal growth factor, desmosomal proteins, and cytokeratins). In conclusion, primary cultures developed from normal human conjunctiva maintained the epithelial characteristics in vitro. Because the conjunctiva is a major component of the anterior ocular surface, we propose this in vitro system as suitable for physiopathologic and toxicologic studies.