title: MALDI Imaging Mass Spectrometry Spatially Maps Age-Related Deamidation and Truncation of Human Lens Aquaporin-0.
abstract: OBJECTIVE
  To spatially map human lens Aquaporin-0 (AQP0) protein modifications, including lipidation, truncation, and deamidation, from birth through middle age using matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS).
  
  
  METHODS
  Human lens sections were water-washed to facilitate detection of membrane protein AQP0. We acquired MALDI images from eight human lenses ranging in age from 2 months to 63 years. In situ tryptic digestion was used to generate peptides of AQP0 and peptide images were acquired on a 15T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. Peptide extracts were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and database searched to identify peptides observed in MALDI imaging experiments.
  
  
  RESULTS
  Unmodified, truncated, and fatty acid-acylated forms of AQP0 were detected in protein imaging experiments. Full-length AQP0 was fatty acid acylated in the core and cortex of young (2- and 4-month) lenses. Acylated and unmodified AQP0 were C-terminally truncated in older lens cores. Deamidated tryptic peptides (+0.9847 Da) were mass resolved from unmodified peptides by FTICR MS. Peptide images revealed differential localization of un-, singly-, and doubly-deamidated AQP0 C-terminal peptide (239-263). Deamidation was present at 4 months and increases with age. Liquid chromatography-MS/MS results indicated N246 undergoes deamidation more rapidly than N259.
  
  
  CONCLUSIONS
  Results indicated AQP0 fatty acid acylation and deamidation occur during early development. Progressive age-related AQP0 processing, including deamidation and truncation, was mapped in human lenses as a function of age. The localization of these modified AQP0 forms suggests where AQP0 functions may change throughout lens development and aging.
authors.forename: Jamie L
authors.initials: JL
authors.lastname: Wenke
authors.forename: Kristie L
authors.initials: KL
authors.lastname: Rose
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Spraggins
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Schey
mesh_terms: D000328:Adult; D000375:Aging / Q000378:metabolism*; D020346:Aquaporins / Q000378:metabolism*; D002386:Cataract / Q000378:metabolism*; D005136:Eye Proteins / Q000378:metabolism*; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D007908:Lens, Crystalline / Q000737:chemistry*; D008297:Male; D008875:Middle Aged; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*; D055815:Young Adult
chemical_list: D020346:Aquaporins; D005136:Eye Proteins; C030328:aquaporin 0