SPARC-null vs. wild-type lens epithelium

SPARC is a matricellular glycoprotein involved in regulation of the extracellular matrix, growth factors, adhesion, and migration. SPARC-null mice have altered basement membranes and develop posterior sub-capsular cataracts with cell swelling and equatorial vacuoles. Exchange of fluid, nutrients, and waste products in the avascular lens is driven by a unique circulating ion current. Here we demonstrate that SPARC-null mouse lenses exhibit abnormal circulation of fluid, ion, and small molecules which leads to altered fluorescein distribution in vivo, loss of resting membrane polarization, and altered distribution of small molecules. Microarray analysis of SPARC-null lenses showed changes in gene expression of ion channels and receptors, matrix and adhesion genes, cytoskeleton, immune response genes, and cell signaling molecules. Our results demonstrate that the regulation of SPARC on cell-capsular matrix interactions can influence the circulation of fluid and ions in the lens, and the phenotype in the SPARC-null mouse lens is the result of multiple intersecting pathways. Lens epithelial cells from 7 lenses of littermate mice were isolated by laser capture microdissection. 3 wild-type lenses from 3 different mice and 4 knock-out lenses from 3 different mice were used as biological replicates.