The role of endogenous epidermal growth factor receptor ligands in mediating corneal epithelial homeostasis.
OBJECTIVE
To provide a comprehensive study of the biological role and therapeutic potential of six endogenous epidermal growth factor receptor (EGFR) ligands in corneal epithelial homeostasis.


METHODS
Kinetic analysis and dose response curves were performed by using in vitro and in vivo wound-healing assays. Biochemical assays were used to determine receptor expression and activity. Human tears were collected and quantitatively analyzed by multianalyte profiling for endogenous EGFR ligands.


RESULTS
Epidermal growth factor receptor ligands improved wound closure and activated EGFR, but betacellulin (BTC) was the most efficacious promoter of wound healing in vitro. In contrast, only epidermal growth factor (EGF) promoted wound healing in vivo. Human tears from 25 healthy individuals showed EGFR ligands at these average concentrations: EGF at 2053 ± 312.4 pg/mL, BTC at 207 ± 39.4 pg/mL, heparin-binding EGF at 44 ± 5.8 pg/mL, amphiregulin at 509 ± 28.8 pg/mL, transforming growth factor-α at 84 ± 19 pg/mL, and epiregulin at 52 ± 15 pg/mL.


CONCLUSIONS
Under unwounded conditions, only EGF was present at concentrations near the ligand's Kd for the receptor, indicating it is the primary mediator of corneal epithelial homeostasis. Other ligands were present but at concentrations 11- to 7500-fold less their Kd, preventing significant ligand binding. Further, the high levels of EGF and its predicted binding preclude receptor occupancy by exogenous ligand and can explain the discrepancy between the in vitro and in vivo data. Therefore, therapeutic use of EGFR ligands may be unpredictable and impractical.
Department of Pharmacology and Toxicology, University of Louisville School of Medicine, Louisville, Kentucky, United States.
Joanne L
JL
Peterson
Eric D
ED
Phelps
Mark A
MA
Doll
Shlomit
S
Schaal
Brian P
BP
Ceresa
D000328:Adult; D000818:Animals; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000187:drug effects; D019573:Epithelium, Corneal / Q000502:physiology*; D066246:ErbB Receptors / Q000502:physiology*; D005260:Female; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D008024:Ligands; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008875:Middle Aged; D008954:Models, Biological; D013666:Tears / Q000378:metabolism; D014945:Wound Healing / Q000187:drug effects / Q000502:physiology; D055815:Young Adult
D008024:Ligands; D066246:ErbB Receptors
EGF; EGFR; HB-EGF; betacellulin