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Published on: May 12, 2011
The molecular basis of neurotrophic keratitis
1Center for sight, Georgetown University Medical Center Washington, DC.
Abstract:
Endogenous proliferation of corneal epithelial cells is regulated by a bidirectional control process characterized by an adrenergic, cAMP-dependent 'off', and a cholinergic, muscarinic cGMP-dependent 'on' response. The adrenergic receptor(s) are located in the plasma membrane (microsomal fraction), whereas the novel feature of the system is a cholinergic receptor specific for acetylcholine (ACH) located in the nuclear membrane. Exogenous substances which raise intracellular cAMP levels such as isoproterenol or PGE1, shut off epithelial mitosis: and, carbamylcholine or ACH raise intranuclear cGMP levels and increase mitosis by specific, regulatory stimulation of RNA-polymerase II activity. We believe that this regulatory system explains the transitory mitotic suppression induced by superficial corneal wounding (interruption of adrenergic fibres, chalone-effect); and the marked, permanent depression of epithelial mitosis associated with decreased intracellular ACH levels which are produced by total corneal denervation, and which results in neurotrophic keratitis.
Insights
Corneal epithelial cell growth is controlled by opposing adrenergic (off) and cholinergic (on) signals. This system explains wound-induced mitosis suppression and neurotrophic keratitis.
Area of Science:
- Ophthalmology
- Cell Biology
- Molecular Biology
Background:
- Corneal epithelial cell proliferation is crucial for maintaining ocular surface integrity.
- Regulation involves complex signaling pathways influencing cell division.
Purpose of the Study:
- To elucidate the bidirectional regulatory mechanisms controlling corneal epithelial cell mitosis.
- To identify the roles of adrenergic and cholinergic pathways in cell proliferation.
Main Methods:
- Investigated adrenergic and cholinergic receptor localization and function.
- Assessed the impact of cAMP and cGMP modulation on mitosis.
- Examined the role of acetylcholine (ACH) and RNA-polymerase II activity.
Main Results:
- Adrenergic signaling via cAMP inhibits mitosis; cholinergic signaling via cGMP stimulates mitosis.
- Cholinergic receptors are located in the nuclear membrane, regulating RNA-polymerase II.
- Exogenous cAMP-raising agents (isoproterenol, PGE1) suppress mitosis; cholinergic agents (carbachol, ACH) increase mitosis.
Conclusions:
- A bidirectional adrenergic-cholinergic system regulates corneal epithelial cell proliferation.
- Nuclear membrane cholinergic receptors play a novel role in controlling mitosis.
- This system explains mitotic suppression after wounding and in neurotrophic keratitis.
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