Fate of cystatin C lacking the leader sequence in RPE cells.

The study made use of transiently transfected RPE cells expressing mature cystatin C (lacking the 26 amino acids leader sequence of the precursor cystatin C) fused to enhanced green fluorescent protein (EGFP) and, in control transfections, EGFP on its own. The findings demonstrate that 'leaderless' cystatin C is not processed through the secretory pathway of RPE cells. Since a polymorphism in the leader sequence has recently been associated with increased risk for development of exudative age-related macular degeneration (AMD), the present findings lend support to the hypothesis that impairment of function of the leader sequence may contribute to the aetiology of exudative AMD.