Latent TGF-β binding protein-2 is essential for the development of ciliary zonule microfibrils

Hum Mol Genet. 2014 Nov 1;23(21):5672-82. doi: 10.1093/hmg/ddu283. Epub 2014 Jun 6.

Abstract

Latent TGF-β-binding protein-2 (LTBP-2) is an extracellular matrix protein associated with microfibrils. Homozygous mutations in LTBP2 have been found in humans with genetic eye diseases such as congenital glaucoma and microspherophakia, indicating a critical role of the protein in eye development, although the function of LTBP-2 in vivo has not been well understood. In this study, we explore the in vivo function of LTBP-2 by generating Ltbp2(-/-) mice. Ltbp2(-/-) mice survived to adulthood but developed lens luxation caused by compromised ciliary zonule formation without a typical phenotype related to glaucoma, suggesting that LTBP-2 deficiency primarily causes lens dislocation but not glaucoma. The suppression of LTBP2 expression in cultured human ciliary epithelial cells by siRNA disrupted the formation of the microfibril meshwork by the cells. Supplementation of recombinant LTBP-2 in culture medium not only rescued the microfibril meshwork formation in LTBP2-suppressed ciliary epithelial cells but also restored unfragmented and bundled ciliary zonules in Ltbp2(-/-) mouse eyes under organ culture. Although several reported human mutant LTBP-2 proteins retain normal domain structure and keep the fibrillin-1-binding site intact, none of these mutant proteins were secreted from their producing cells, suggesting secretion arrest occurred to the LTBP-2 mutants owing to conformational alteration. The findings of this study suggest that LTBP-2 is an essential component for the formation of microfibril bundles in ciliary zonules.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Cilia / genetics*
  • Ectopia Lentis / genetics
  • Ectopia Lentis / pathology
  • Epithelial Cells / metabolism
  • Epithelial Cells / pathology
  • Fibrillin-1
  • Fibrillins
  • Gene Knockout Techniques
  • Gene Targeting
  • Genotype
  • Glaucoma / genetics
  • Humans
  • Latent TGF-beta Binding Proteins / genetics*
  • Latent TGF-beta Binding Proteins / metabolism
  • Mice
  • Mice, Knockout
  • Microfibrils / genetics*
  • Microfilament Proteins / metabolism
  • Mutation
  • Phenotype
  • Protein Binding

Substances

  • FBN1 protein, human
  • Fbn1 protein, mouse
  • Fibrillin-1
  • Fibrillins
  • LTBP2 protein, human
  • Latent TGF-beta Binding Proteins
  • Microfilament Proteins