Patterned expression of neurotrophic factors and receptors in human limbal and corneal regions.
OBJECTIVE
To evaluate the expression patterns of neurotrophic factors (NTFs) and their receptors in the human cornea with the intention of exploring the role of NTFs in maintaining corneal epithelial stem cells in the limbus.


METHODS
Fresh human corneoscleral tissues were prepared for frozen sections. Immunofluorescent staining was performed with primary antibodies against six members of three NTF families and their six receptors. To confirm the specificity of NTF primary antibodies, neutralization experiments with their corresponding peptides and western blot analysis were performed.


RESULTS
Based on spatial and differential immuno-localization, three patterns of NTF expression were potentially involved in epithelial-mesenchymal interaction on the ocular surface: (1) the epithelial type: nerve growth factor (NGF) and glial cell-derived neurotrophic factor (GDNF); (2) the paracrine type: neurotrophin (NT)-3 and NT-4/5; and (3) the reciprocal type: brain-derived neurotrophic factor (BDNF). The stem cell-enriched basal cells of the limbal epithelium expressed three unique staining patterns for NTFs: (1) exclusively positive for NGF, GDNF, and their corresponding receptors, TrkA and GDNF family receptor alpha (GFRalpha)-1; (2) relatively high levels of BDNF; and (3) negative for NT-3 and NT-4. Additionally, the neurotrophin common low-affinity receptor, p75NTR, was mainly expressed by the basal layer of the entire corneal and limbal epithelia, and TrkB and TrkC were evenly expressed by the entire corneal and limbal epithelia. BDNF, p75NTR, TrkB, and TrkC are also abundantly expressed by limbal stroma cells. No specific immunoreactivity to ciliary neurotrophic factor (CNTF) and its receptor, CNTFRalpha, was detected in cornea tissue in situ.


CONCLUSIONS
Our findings revealed patterned expression of NTFs and their receptors in the human ocular surface, suggesting that they may play a vital role in maintaining corneal epithelial stem cells in the limbus. NGF, GDNF, GFRalpha-1, TrkA, and BDNF may serve as new limbal basal cell markers defining the corneal epithelial stem cell phenotype.
Qi
Hong
H
Ocular Surface Center, Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, TX 77030, USA.
Chuang
Eliseu Yung
EY
Yoon
Kyung-Chul
KC
de Paiva
Cintia S
CS
Shine
H David
HD
Jones
Dan B
DB
Pflugfelder
Stephen C
SC
Li
De-Quan
DQ
D015153:Blotting, Western; D003315:Cornea / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000378:metabolism; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D016850:Limbus Corneae / Q000378:metabolism*; D009414:Nerve Growth Factors / Q000378:metabolism*; D017475:Receptors, Nerve Growth Factor / Q000378:metabolism*; D014018:Tissue Distribution
D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D009414:Nerve Growth Factors; D017475:Receptors, Nerve Growth Factor