Neurturin-deficient mice develop dry eye and keratoconjunctivitis sicca.
OBJECTIVE
Neurturin has been identified as a neurotrophic factor for parasympathetic neurons. Neurturin-deficient (NRTN(-/-)) mice have defective parasympathetic innervation of their lacrimal glands. This study was conducted to evaluate tear function and ocular surface phenotype in NRTN(-/-) mice.


METHODS
Determined by tail genomic DNA PCR, 25 NRTN(-/-) mice and 17 neurturin-normal (NRTN(+/+)) mice aged 6 weeks to 4 months were evaluated. Aqueous tear production, tear fluorescein clearance and corneal sensation were serially measured. Corneal permeability to AlexaFluor dextran (AFD; Molecular Probes, Eugene, OR) was measured by a fluorometric assay at 485 nm excitation and 530 nm emission. Histology was evaluated in PAS-stained sections. Mucin and HLA class II (IA) antigen were assessed by immunofluorescent staining. Tear IL-1beta was measured by ELISA, and tear matrix metalloproteinase (MMP)-9 by zymography. Gene expression in the corneal epithelia was analyzed by semiquantitative RT-PCR.


RESULTS
In comparison to that in age-matched NRTN(+/+) mice, aqueous tear production, tear fluorescein clearance, and corneal sensation were significantly reduced in NRTN(-/-) mice, whereas corneal permeability to AFD was significantly increased. Immunoreactive MUC-4 and -5AC mucin and goblet cell density (P < 0.001) in the conjunctiva of NRTN(-/-) mice were lower than in NRTN(+/+) mice. The expression of MUC-1 and -4 mRNA by the corneal epithelium was reduced in NRTN(-/-) mice. There were a significantly greater number of IA antigen-positive conjunctival epithelial cells in NRTN(-/-) mice than NRTN(+/+) mice. Tear fluid IL-1beta and MMP-9 concentrations and the expression of IL-1beta, TNF-alpha, macrophage inflammatory protein (MIP)-2, cytokine-induced neutrophil chemoattractant (KC), and MMP-9 mRNA by the corneal epithelia were significantly increased in NRTN(-/-) mice, compared with NRTN(+/+) mice.


CONCLUSIONS
Neurturin-deficient mice show phenotypic changes and ocular surface inflammation that mimic human keratoconjunctivitis sicca. This model supports the importance of a functional ocular surface-central nervous system-lacrimal gland sensory-autonomic neural network in maintaining ocular surface health and homeostasis.
D000818:Animals; D002452:Cell Count; D003315:Cornea / Q000378:metabolism; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D019793:Fluorescein / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D015590:Fluorophotometry; D020397:Goblet Cells / Q000166:cytology; D000949:Histocompatibility Antigens Class II / Q000378:metabolism; D007375:Interleukin-1 / Q000378:metabolism; D007637:Keratoconjunctivitis / Q000209:etiology* / Q000378:metabolism* / Q000473:pathology; D007765:Lacrimal Apparatus / Q000378:metabolism*; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009077:Mucins / Q000235:genetics / Q000378:metabolism; D009414:Nerve Growth Factors / Q000172:deficiency* / Q000235:genetics; D051101:Neurturin; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013666:Tears / Q000378:metabolism*
D000949:Histocompatibility Antigens Class II; D007375:Interleukin-1; D009077:Mucins; D009414:Nerve Growth Factors; D051101:Neurturin; C495056:Nrtn protein, mouse; D020780:Matrix Metalloproteinase 9; D019793:Fluorescein