European Association for Vision and Eye Research

Purpose: Sparc is a calcium, hydroxyapatite and collagen binding protein which is implicated in cell proliferation, tissue morphogenesis and repair. Sparc null mice show sub-cortical posterior cataract formation and eventual rupture of the lens capsule after six months of age. We have carried out microarrays on embryonic eyes and adult lenses from these mice at various ages, with the aim of identifying genes involved in the progression of disease.

Methods: Array studies were carried out using E14.5 eyes, 4 month and 9 month old lenses from Sparc null mice and age, strain and sex matched controls, using the 15k mouse NIA clone set. Differentially regulated genes were selected from multiple repetitions; these were checked for differential gene expression using semi-quantitative RT-PCR.

Results: Using primers specific to different haemoglobin genes, we have confirmed the downregulation of multiple murine haemoglobin mRNAs in the lenses of 9-month old Sparc null mice as compared with controls. Another downregulated gene, EraF, is involved in the correct folding of haemoglobin proteins. Other genes confirmed to date include Sparc itself, collagen sub-types, metallothionein 2 and glypican-3. Glypican-3 causes Simpson-Golabi-Behmel syndrome; when mutated; symptoms of this disorder include age-onset cataracts.

Conclusions: We have confirmed the expression of haemoglobins in the murine lens. Haemoglobins may have a role in apoptosis, the maintenance of lens structure, oxygen transport and/or oxygen buffering in the lens; their downregulation as a result of Sparc loss may play a role in the pathogenesis of age-onset cataract in these mice.