Syndecan-1-mediated loading of VEGF-A into small extracellular vesicles facilitates peritubular capillary repair during AKI-to-CKD transition

Acute kidney injury (AKI) is a severe clinical event with a high risk of transitioning to chronic kidney disease (CKD). Persistent hypoxia resulting from peritubular capillaries (PTCs) loss is a key factor driving this chronic transition. However, the mechanisms governing PTCs injury and repair, particularly under different AKI severity, remain unclear. This study demonstrates that small extracellular vesicle (sEV) carried VEGF-A as an essential regulator of PTCs repair and decreased as the severity of tubular injury increased. We found that VEGF-A was sorted into sEV via syndecan-1 (SDC-1), attaching to the heparan sulfate chain in moderate AKI. SDC-1 knockdown in renal tubules significantly reduced VEGF-A packaging into EVs and aggravated PTCs rarefaction and renal fibrosis. Overexpression of SDC-1 promoted the production of VEGF-A⁺ sEV and their proliferative effects on endothelial cells. These findings demonstrate that SDC-1 contributes to the secretion of VEGF-A⁺ sEV from moderately injured tubules, facilitating PTCs repair after AKI.