Insulin-like growth factor binding protein-5 expression by human trabecular meshwork

Invest Ophthalmol Vis Sci. 1998 Jan;39(1):45-53.

Abstract

Purpose: The authors found transcript expression for insulin-like growth factor binding protein-5 (IGFBP-5) while screening for uniquely expressed trabecular meshwork (TM) mRNAs. Because the insulin-like growth factor (IGF) autocrine-paracrine system may provide an important signaling mechanism between TM cells and the outflow pathway, the expression of IGFBP-5 and IGF-I receptor in the TM was characterized.

Methods: Poly(A+) RNA was isolated from cell cultures of human TM, ciliary body, retinal pigment epithelium, and skin fibroblasts and subjected to reverse transcription-polymerase chain reaction (RT-PCR) differential display analysis. A unique 980-bp band present in the TM was cloned and sequenced. Additional PCR and Northern analyses were used to define trabecular IGFBP-5 expression. Western immunoblots and confocal immunohistochemistry were used to evaluate the protein expression patterns of IGFBP-5 and the IGF-I receptor. IGF-I and IGF-II were added to trabecular cells in culture, and matrix metalloproteinase production was evaluated.

Results: A unique differential display band was identified in the TM. Sequencing of this band identified it as the 3'-untranslated region of IGFBP-5. RT-PCR, using a variety of specific primers for IGFBP-5, Northern analysis, Western immunoblots, and immunohistochemical analysis, confirmed that IGFBP-5 was expressed in the TM. However, IGFBP-5 was also present at low levels in the ciliary body and skin fibroblasts by Northern and Western analysis, in contrast with the differential display findings. In addition, the IGF-I receptor was expressed by the TM and showed cell-surface staining by immunohistochemistry. Trabecular IGFBP-5 was distributed throughout the meshwork in the extracellular matrix and the cells with more staining in the juxtacanalicular region than in the uveal meshwork. IGF-I, but not IGF-II, modestly increased trabecular stromelysin and gelatinase B but not collagenase, gelatinase A, or tissue inhibitor of metalloproteinases 1 or 2.

Conclusions: IGFBP-5 and IGF-I receptor were expressed at significant levels by TM cells and may serve an important role in trabecular function.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Blotting, Northern
  • Blotting, Western
  • Cells, Cultured
  • DNA Primers
  • Extracellular Matrix / metabolism
  • Fluorescent Antibody Technique, Indirect
  • Humans
  • Insulin-Like Growth Factor Binding Protein 5 / genetics
  • Insulin-Like Growth Factor Binding Protein 5 / metabolism*
  • Insulin-Like Growth Factor I / pharmacology
  • Insulin-Like Growth Factor II / pharmacology
  • Metalloendopeptidases / metabolism
  • Microscopy, Confocal
  • Polymerase Chain Reaction
  • RNA / isolation & purification
  • RNA, Messenger / metabolism
  • Receptor, IGF Type 1 / genetics
  • Receptor, IGF Type 1 / metabolism*
  • Trabecular Meshwork / cytology
  • Trabecular Meshwork / drug effects
  • Trabecular Meshwork / metabolism*

Substances

  • DNA Primers
  • Insulin-Like Growth Factor Binding Protein 5
  • RNA, Messenger
  • RNA
  • Insulin-Like Growth Factor I
  • Insulin-Like Growth Factor II
  • Receptor, IGF Type 1
  • Metalloendopeptidases