Up-regulation of osteonectin/SPARC in age-related cataractous human lens epithelia.

PURPOSE To characterize gene expression patterns between epithelia isolated from cataractous and normal human lenses. METHODS Reverse transcriptase differential display was used to identify differential expression between cataractous and normal epithelia. RT-PCR was used to compare pooled and individual RNA samples. RESULTS One transcript, up-regulated in cataractous as compared to normal epithelia, was identified as osteonectin which is also known as SPARC (secreted acidic protein rich in cysteines). RT-PCR confirmed over-expression of this RNA. High levels of osteonectin mRNA were also detected in six individual epithelia dissected from cataractous lenses. CONCLUSIONS The present study provides evidence for up-regulation of osteonectin in human age-related cataract and suggests that osteonectin, a protein involved in cell-cycle control, extracellular matrix and Ca++ binding, plays an important role in human lens homeostasis and may be involved in processes leading to lens opacity.