CKAP4 in Extracellular Vesicle-Derived From Podocyte Serves as a Non-Invasive Diagnostic Biomarker for Diabetic Nephropathy and Promotes Vascular Calcification.

Reliable non-invasive biomarkers for early detection of diabetic nephropathy (DN), a leading cause of chronic kidney disease, remain limited. In this study, we isolate urinary extracellular vesicles (uEVs) using wheat germ agglutinin (WGA)-conjugated magnetic beads and identify cytoskeleton-associated protein 4 (CKAP4) as a potential diagnostic biomarker for DN. Proteomic profiling and flow cytometry show that CKAP4 levels are significantly higher in uEVs from DN patients than in those from diabetic, non-diabetic renal disease (NDRD) and healthy control groups. Receiver operating characteristic (ROC) analysis demonstrates excellent diagnostic performance, with area under the curve (AUC) values of 0.9998 (sensitivity = 98.77%, specificity = 100%) for DN versus controls, and 0.9859 (sensitivity = 95.72%, specificity = 99.24%) for DN versus diabetes mellitus. CKAP4 levels, elevated even at early-stage DN, positively correlate with glomerulosclerosis, increasing with the severity of interstitial fibrosis and tubular atrophy (IFTA). Mechanistically, CKAP4-containing EVs derived from high glucose-treated podocytes promote vascular calcification in vascular smooth muscle cells via YAP signalling. These findings identify CKAP4 in podocyte-derived uEVs as a robust non-invasive biomarker for early DN detection and provide new insights into the vascular pathology associated with the disease.