Abstract
Purpose :
Limbal stem cell deficiency (LSCD) is characterized by the loss of limbal epithelial stem cells, resulting in a pathological process termed ‘conjunctivalization’ which compromises corneal transparency, leading to blindness. Current diagnosis for LSCD is limited because reliable conjunctiva-specific biomarkers are lacking. This study sought to address this shortcoming through the serendipitous discovery of insulin-like growth factor binding protein (IGFBP)-7.
Methods :
To assess the validity of IGFBP-7 as a conjunctival specific protein, its expression was determined in normal (n=83) and conjunctivalized (n=52) mouse corneas with experimentally-induced LSCD, and in normal cadaveric human corneas (n=7) and human pterygia (n=15); a disease characterized by invasion of a conjunctivalized, fibrovascular pannus. Clinical assessments including slit-lamp microscopy, fluorescein staining and impression cytology, and laboratory-based biochemical, molecular and immunological assays were conducted in a complimentary manner.
Results :
Mass spectrometry of conditioned media from murine ocular surface tissue explants revealed IGFBP-7 as a relatively abundant protein. Its expression was detected in normal conjunctival epithelium and conjunctivalized corneas from mice with LSCD, and in human pterygium epithelium but not in normal mouse or human corneal epithelium. In LSCD mice, IGFBP-7 expression was increased 2.9-fold at 4-weeks post-disease induction compared to steady-state (73.87% vs 26.13%; p<0.0001). Impression cytology specimens from LSCD mice displayed a 1.6-fold increased IGFBP-7 expression at 8-weeks post-LSCD compared to steady-state (61.40% vs 39.60%; p=0.0464). Both IGFBP-7 and Muc5AC (a conjunctiva-specific marker) had a similar distribution and were found in comparable quantities after LSCD initiation; however, IGFBP-7 was detected ~2-weeks earlier.
Conclusions :
This study has provided novel insights into the specificity of IGFBP-7 for the mammalian conjunctival epithelium in health and disease. The advantages of IGFBP-7 include its small molecular size, soluble-secreted format, and non-reliance on goblet cells. A point-of-care test for IGFBP-7 could be developed to assist clinicians in early diagnosis, and to monitor disease progression, severity and therapeutic outcomes in patients with LSCD.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.