Oral Presentation HUPO 2019 - 18th Human Proteome Organization World Congress

Visualising the physiological biochemistry of human ocular lens transparency and cataract with imaging mass spectrometry (#57)

Gus Grey 1 , Rebecca Perwick 1 , George Guo 1 , Nicholas Demarais 1 , Mitchell Nye-Wood 1 , Ivy Li 1 , Julie Lim 1 , Paul Donaldson 1
  1. University of Auckland, Auckland, New Zealand

To function as an effective optical element, the avascular lens exhibits several specialisations that include an ordered cellular structure, a gradient in refractive index, and a circulating current to deliver nutrients and remove waste products from the lens nucleus. The aging lens undergoes many changes to metabolites and proteins that alter these physiological and optical functions in specific lens regions, leading to the formation of age-related nuclear (ARN) cataract. A combination of human and laboratory-aged bovine lenses have been analysed by advanced mass spectrometry techniques to spatially map these changes and understand how they contribute to ARN cataract formation at the whole organ level.

A range of human lens ages (29y-82y) or bovine lenses, either laboratory-aged by hyperbaric oxygen treatment or organ cultured in artificial aqueous humour containing stable isotopically-labelled metabolites, were analyzed. Axial cryosections (20um) of lenses were collected on MALDI targets, and matrix applied by a TM-Sprayer. Positive ion mode MALDI-TOF (for proteins) or negative ion mode MALDI-FT-ICR (for metabolites) imaging mass spectrometry (IMS) was used to map the distribution of protein and metabolite distributions in each lens at 150um spatial resolution. SCiLS lab software was used to visualise and quantify age-related changes to mass spectral signals. GC-MS and LC-MS/MS approaches were used to validate distributions detected by IMS.

Several age-related modifications to proteins were observed in specific regions of the lens. For example, glutathione modified beta and gamma crystallins at specific sites, while a corresponding decrease in reduced glutathione levels was detected in the lens core. Additional alterations in lipid and UV filter levels and distributions were spatially mapped. Initial experiments to assess the role of the lens circulating current in lens metabolite transport established IMS as an imaging approach that could be utilised in developing future therapeutic interventions to delay the onset of lens cataract.