Refining the Composition and Significance of Human Kidney Intratubular Casts Using Spatial Protein Imaging

Area of Science:

• Nephrology
• Renal Pathology
• Biomarker Discovery

Background:

• Kidney intratubular casts are common in distal nephron segments and associated with kidney disease.
• The composition and pathological significance of these casts remain understudied.

Purpose of the Study:

• To investigate the protein composition of kidney intratubular casts.
• To determine the association between cast composition and tubular injury.
• To explore the potential of urinary Prominin-1 (PROM1) as an acute kidney injury (AKI) biomarker.

Main Methods:

• Utilized Hematoxylin and Eosin (H&E) staining and Co-detection by indexing (CODEX) multiplexed spatial protein imaging on human kidney biopsies.
• Analyzed intratubular casts from the Kidney Precision Medicine Project (KPMP).
• Performed immunoblotting for urinary PROM1 and assessed publicly available urinary proteomics data.

Main Results:

• Identified PROM1 and insulin-like growth factor binding protein 7 (IGFBP7) as major cast constituents, alongside uromodulin (UMOD).
• Observed a significant loss of sodium-chloride cotransporter (NCC) and aquaporin-2 (AQP2) expression in tubules with casts, correlating with cast protein content.
• Found elevated urinary PROM1 levels in patients with AKI compared to healthy controls, with intra-cast PROM1 strongly associated with tubular injury (OR 26.7).

Conclusions:

• Prominin-1 (PROM1), an epithelial cell dedifferentiation and injury marker, is a novel major component of kidney intratubular casts.
• Cast protein composition varies with disease state and is linked to distal nephron tubular injury.
• Urinary PROM1 shows potential as a valuable biomarker for detecting acute kidney injury (AKI).