INSULIN-LIKE GROWTH-FACTOR-I PROMOTES CELL-PROLIFERATION IN THE ABSENCE OF MODULATION OF COLLAGEN PHENOTYPES AND UTILIZES IRS-1, NOT PLC-GAMMA-1, IN CORNEAL ENDOTHELIAL-CELLS

Corneal endothelial cells are differentiated cells and are thus incapa ble of physiologic regeneration. In a search for a growth factor that would promote optimal proliferation of corneal endothelial cells in th e absence of other modulating activities, the effect of insulin-like g rowth factor-I (IGF-I) on rabbit corneal endothelial cells was studied . In addition, cellular effector molecules responsible for the signal pathway for IGF-I were studied. IGF-I at 50 ng/ml stimulated corneal e ndothelial cell proliferation after at least 8 h of treatment. IGF-I d id not change cell shape of corneal endothelial cells: the cells treat ed with IGF-I at 50 ng/ml maintained polygonal morphology regardless o f the duration of exposure. IGF-I did not alter collagen phenotypes ei ther qualitatively or quantitatively: the treated cells continued to s ynthesize types IV and VIII collagen, as did the control cells. The st eady-state levels of alpha 2(I) collagen RNA and alpha 2(IV) RNA were not altered by IGF-I treatment. Immunohistochemical analysis showed th at IGF-I is present in corneal endothelium in vivo, while the underlyi ng Descemet's membrane demonstrated no staining. Corneal endothelial c ells also produce IGF binding protein-2 (IGFBP-2), which appears to bi nd IGF-I that has been introduced exogenously in the medium. Further i nvestigation as to how the signals of IGF-I were transmitted for the b iological activities demonstrated that the expression of insulin recep tor substrate-1 (IRS-1) is up-regulated by IGF-I treatment, while PLC- gamma 1 expression is not altered by this growth factor. These finding s suggest that IGF-I may be an appropriate growth factor to promote co rneal endothelial cell proliferation without inducing other modulating effects that can lead to corneal fibrosis.