Spatial proteomics to discover aging-associated alterations in the renal tubulointerstitium.

The preservation of tissue architecture and morphology in formalin-fixed paraffin-embedded (FFPE) tissues enables spatial resolution at the cellular and sub-cellular levels. Laser capture microdissection (LCM) combined with liquid chromatography tandem mass spectrometry analysis permits collection of tissue areas with spatial context for proteome profiling from FFPE slides. In this study, we performed proteome profiling of non-diseased renal tubulointerstitial tissue in a cohort of young (< 40 years) and old (> 70 years) individuals with the goal of spatially correlating the histomorphology to the proteomic profile. To perform in-depth characterization of renal tubulointerstitium and to identify renal aging-associated proteins, a multiplexing strategy using tandem mass tags (TMT) was employed, resulting in the quantitation of 7,355 proteins. Our approach allowed for identification of proteins with low abundance such as fibrocystin and ninein-like protein. Notably, 162 solute carrier proteins from 47 solute carrier families were identified, which were enriched in proximal and distal tubule cells. Finally, we discovered a proteomic signature associated with renal aging, which includes metalloproteinase inhibitor 3, nicotinamide N-methyltransferase, matrix metallopeptidase 7, phenazine biosynthesis-like domain-containing protein and solute carrier family 23 member 1. Overall, our study demonstrates the power of LCM combined with proteomics to leverage archived FFPE tissue samples for investigating proteomic alterations in the renal tubulointerstitium with age at a high depth of proteome coverage.