Function of the tryptophan metabolite, L-kynurenine, in human corneal endothelial cells.
OBJECTIVE
Penetrating keratoplasty has been the mainstay for the treatment of blindness and is the most common form of tissue transplantation worldwide. Due to significant rates of rejection, treatment of immunological transplant reactions is of wide interest. Recently in a mouse model, the overexpression of indoeleamine 2,3 dioxigenase (IDO) was led to an extension in corneal allograft survival. L-kynurenine is a tryptophan metabolite, which may render activated T-cells apoptotic and therefore might modulate an allogenous transplant reaction. The function of L-kynurenine in the human cornea remains unclear. We analyzed the expression levels of IDO in human corneal endothelial cells (HCECs) and downstream tryptophan/kynurenine mechanisms in cell culture.


METHODS
An immunological activation profile was determined in proliferation assays of monocytes from healthy donors. Reversed-phase high pressure liquid chromatography (HPLC), western blot, real time polymerase chain reaction (PCR), and microarray analyses were used. The expression of IDO and immunological infiltration of rejected human corneal allografts (n=12) were analyzed by immunohistochemistry.


RESULTS
We found IDO and an associated tryptophan/kynurenine transporter protein exchange mechanism upregulated by inflammatory cytokines in HCECs. The inhibition of T-cell proliferation might depend on rapid delivery of the tryptophan metabolite, L-kynurenine, to the local corneal environment. Microarray analysis gives evidence that the large amino acid transporter 1 (LAT1) transporter protein is responsible for this mechanism.


CONCLUSIONS
Our data support that adequate levels of functional L-kynurenine might contribute to the maintenance of a relative immune privilege in the ocular anterior chamber, thereby contributing to the preservation of corneal allogeneic cells.
Serbecic
Nermin
N
Department of Ophthalmology, Medical University of Vienna, Vienna, Austria. nermin.serbecic@meduniwien.ac.at
Lahdou
Imad
I
Scheuerle
Alexander
A
Höftberger
Romana
R
Aboul-Enein
Fahmy
F
D017209:Apoptosis / Q000187:drug effects; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D017077:Culture Media, Conditioned; D016207:Cytokines / Q000494:pharmacology; D004728:Endothelium, Corneal / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D004797:Enzyme-Linked Immunosorbent Assay; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006684:HLA-DR Antigens / Q000235:genetics / Q000378:metabolism; D059811:HLA-DRB1 Chains; D006801:Humans; D007150:Immunohistochemistry; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase / Q000235:genetics / Q000378:metabolism; D007249:Inflammation / Q000473:pathology; D007737:Kynurenine / Q000378:metabolism*; D027283:Large Neutral Amino Acid-Transporter 1 / Q000235:genetics / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D013601:T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D046509:Tissue Culture Techniques; D053781:Transforming Growth Factor beta2 / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects
D017077:Culture Media, Conditioned; D016207:Cytokines; D006684:HLA-DR Antigens; D059811:HLA-DRB1 Chains; D050503:Indoleamine-Pyrrole 2,3,-Dioxygenase; D027283:Large Neutral Amino Acid-Transporter 1; D053781:Transforming Growth Factor beta2; D007737:Kynurenine; D014364:Tryptophan