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Sandrine Le Roux, Marta Urszula Sloniecka, Ludvig Backman, Patrik Danielson; Central and limbal corneal fibroblasts synthesize and secrete Neurokinine A and catecholamines. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5131.
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After a corneal injury, the recovery phase follows an inflammation-proliferation-remodeling scheme, in which corneal fibroblasts undergo apoptosis, proliferate, get activated, and increase their production of extracellular matrix (ECM). The system is regulated by growth factors and cytokines, but other substances are probably also involved at specific levels and could explain the differences of scar formation observed among patients. Indeed, hypercellularity, overproduction of scar tissue, or defects in the remodeling of ECM would lead to corneal haze. Among the candidates, neuropeptides constitute an attractive option. These substances that were initially described as restricted to the neuronal system have since been observed in other tissues. Neurokinin A (NKA), for example, stimulates the proliferation of connective tissue cells in vitro. Furthermore, substance P (SP) stimulates the synthesis and release of pro-inflammatory cytokines by skin fibroblasts and enhances proliferation of tendon fibroblasts as well as corneal epithelial cells. The expression of SP is increased in those tissues in pathological conditions. In this study we investigated whether corneal fibroblasts synthesize and secrete different neuromodulators.
Primary human limbal and central fibroblast cultures were derived from healthy corneas, obtained from donated transplantation graft leftovers. Immunocytochemistry was performed to assess the presence of NKA and tyrosine hydroxylase. The synthesis and secretion of the catecholamines dopamine, norepinephrine (NE), and adrenaline, as well as of NKA and acetylcholine (ACh), were investigated by ELISA or colorimetric assays.
Colorimetric assays revealed that the neuromodulators dopamine, NE, adrenaline, and NKA were synthesized and secreted by the cells, showing a trend towards higher amounts in the limbal cells, with the exception of NE. ACh was also detected in the supernatant of both central and limbal cells. Immunocytochemistry confirmed the presence of NKA and tyrosine hydroxylase, the rate-limiting enzyme of catecholamine synthesis.
Dopamine, NE, adrenaline, NKA, and ACh are all synthesized and secreted by human central and limbal corneal cells in vitro. This observation opens new questions regarding their function in the cornea and their possible role in the scar formation regulation.
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