Spatial Mass Spectrometry-Based Proteomic Analysis of Normal-Appearing Glomeruli from Young and Old Adults.

Background: Kidney aging is characterized by a loss of glomeruli, predominately in the superficial cortex, with a resultant decline in glomerular filtration rate and an increased risk of various kidney-related diseases. The early molecular alterations in glomeruli associated with the aging process are not well studied.

Methods: We combined laser capture microdissection and mass spectrometry-based unbiased proteomic analysis of non-sclerosed, non-ischemic glomeruli in the superficial cortex from young and old adults who underwent a radical nephrectomy for a tumor to understand the age-related molecular changes in glomeruli. 24 young and 30 old adults were used for the discovery dataset and the significant differentially expressed proteins were further validated using an independent set comprising 6 young and 8 old adults.

Results: Kidneys from older adults had lower eGFR, less kidney parenchyma on CT imaging, and more glomerulosclerosis and arteriosclerosis on histology. Quantitative proteomic analysis of non-sclerosed, non-ischemic glomeruli identified increased expression of TIMP3, GPC6, SNCG, APOA4 and NT5E in old adults that were further validated in an independent set. Pathway analysis indicated that proteins with increased expression in old adults were enriched in mitochondrial translational processes, aerobic respiration, and TCA cycle, whereas proteins with decreased expression in old adults were enriched in mRNA splicing, mRNA processing, and nonsense mediated decay. Further, Spearman correlation of validated differentially expressed proteins did not show any significant correlation with the kidney pathology independent of age group.

Conclusions: Overall, this study identified proteins that are specifically associated with the aging process in otherwise normal-appearing glomeruli.