Human Tubulointerstitial Responses to Proteinuria Analysed by Proteomics and Laser Capture Microdissection

Background: Proteinuria damages the tubule compartment. Laser capture microdissection (LCM) enables the precise isolation of specific renal tubular segments, allowing for targeted proteomic analysis of the renal tubular interstitium in IgA nephropathy (IgAN) patients. By identifying differentially expressed proteins and molecular pathways associated with tubulointerstitial injury in IgAN, we sought to gain insights into the pathogenesis of this complex renal disease and identify potential therapeutic targets. Methods: We studied 24 IgAN patients with M1E1 score alongside 10 zero-biopsy controls. Using formalin-fixed paraffin-embedded (FFPE) renal tissue and LCM, we isolated tubular compartments for analysis. Mass spectrometry-based proteomics identified differentially expressed proteins linked to tubulointerstitial injury in IgAN. Results: Our analysis unveiled a distinct proteomic signature characterized by the upregulation of complement system proteins, including C7, C6, C5, and CFHR1, suggestive of an inflammatory response within the tubular interstitium. This inflammatory milieu is further corroborated by the identification of upregulated IgGs. Our study revealed a profound downregulation of sodium ion transporters, SLC5A1 and SLC4A7, within the tubular interstitium of IgAN patients indicating a significant disruption in tubular function. The marked downregulation of these sodium transporters suggests a pivotal role in the pathogenesis of tubulointerstitial injury, potentially contributing to disease severity and renal dysfunction in IgAN. Conclusion: Upregulation of proteins associated with the complement system and immune response outside the glomerular compartment indicates a robust inflammatory process. Downregulation of key sodium ion transporters highlights disrupted electrolyte homeostasis and tubular dysfunction. These insights into tubulointerstitial injury in IgAN enhance our understanding of its pathogenesis and identify potential therapeutic targets to improve renal outcomes.