Revealing proteomic and metabolomic changes associated with lens cataract formation with Imaging Mass Spectrometry (#38)
The lens is a unique structure in the eye that focusses light onto the retina in order to form a sharp image, and has several adaptations to do this effectively. It lacks a blood supply, has an ordered cellular structure, and loses light scattering cellular organelles as lens fibre cells mature. Since it is a large avascular tissue, the lens requires a unique transport system that delivers nutrients and removes waste products from the lens centre. Breakdown of this system is thought to lead to lens protein modification and cataract formation, the leading cause of blindness worldwide. Cataract is characterised by opacities that form in distinct regions of the lens, and results from both genetic and environmental factors. Furthermore, biochemical studies into the aetiology of lens cataract have shown that metabolic changes associated with oxidative damage precede the proteomic changes that lead to cataract formation.
MALDI imaging mass spectrometry was utilised to map metabolomic and proteomic changes that lead to cataract formation in a laboratory model of age-related cataract. Bovine lenses were removed from the ocular globe and subjected to hyperbaric O2 treatment to simulate age-related cataract. Lens cryosections were collected on MALDI targets, and matrix (9-aminoacridine or sinapinic acid) applied. MALDI imaging data sets were collected at 150-250mm spatial resolution using a MALDI-FTICR mass spectrometer (for metabolites) or a MALDI-TOF mass spectrometer (for proteins).
Hundreds of signals for small molecules were detected, including major lens antioxidants, nucleotides and purinergic signalling molecules. For proteomic studies, unmodified and modified forms of the abundant lens protein alpha crystallin were mapped. The effect of hyperbaric oxygen treatment on metabolite and protein distributions will be discussed. This study highlights the complex aetiology of lens cataract and may suggest novel targets for anti-cataract therapies.